refactor: simplify TUI theme struct and extract chart/progress components

Theme simplification (theme/theme.go):
- Remove Purple and BorderHover fields from Theme struct — neither was
  referenced in the new tab renderers, reducing per-theme boilerplate
  from 14 to 12 color definitions

Component extraction (components/):
- Move Sparkline() and BarChart() from card.go to new chart.go, giving
  visualization components their own file as complexity grows
- card.go retains MetricCard, ContentCard, LayoutRow, and CardInnerWidth
  which are layout-focused
- New chart.go: Sparkline (unicode block chars) and BarChart (multi-row
  with anchored Y-axis, optional X-axis labels, dynamic height/width)
- New progress.go: ProgressBar component with customizable width, color,
  and percentage display — used by rate-limit and budget views

Status bar and tab bar updates:
- statusbar.go: adapt to simplified theme struct
- tabbar.go: adapt to simplified theme struct

internal/tui/components/card.go

@@ -1,10 +1,7 @@
+// Package components provides reusable TUI widgets for the cburn dashboard.
 package components
 
 import (
-	"fmt"
-	"math"
-	"strings"
-
 	"cburn/internal/tui/theme"
 
 	"github.com/charmbracelet/lipgloss"
@@ -126,312 +123,3 @@ func CardInnerWidth(outerWidth int) int {
 	}
 	return w
 }
-
-// Sparkline renders a unicode sparkline from values.
-func Sparkline(values []float64, color lipgloss.Color) string {
-	if len(values) == 0 {
-		return ""
-	}
-
-	blocks := []rune{'▁', '▂', '▃', '▄', '▅', '▆', '▇', '█'}
-
-	max := values[0]
-	for _, v := range values[1:] {
-		if v > max {
-			max = v
-		}
-	}
-	if max == 0 {
-		max = 1
-	}
-
-	style := lipgloss.NewStyle().Foreground(color)
-
-	var result string
-	for _, v := range values {
-		idx := int(v / max * float64(len(blocks)-1))
-		if idx >= len(blocks) {
-			idx = len(blocks) - 1
-		}
-		if idx < 0 {
-			idx = 0
-		}
-		result += string(blocks[idx])
-	}
-
-	return style.Render(result)
-}
-
-// BarChart renders a multi-row bar chart with anchored Y-axis and optional X-axis labels.
-// labels (if non-nil) should correspond 1:1 with values for x-axis display.
-// height is a target; actual height adjusts slightly so Y-axis ticks are evenly spaced.
-func BarChart(values []float64, labels []string, color lipgloss.Color, width, height int) string {
-	if len(values) == 0 {
-		return ""
-	}
-	if width < 15 || height < 3 {
-		return Sparkline(values, color)
-	}
-
-	t := theme.Active
-
-	// Find max value
-	maxVal := 0.0
-	for _, v := range values {
-		if v > maxVal {
-			maxVal = v
-		}
-	}
-	if maxVal == 0 {
-		maxVal = 1
-	}
-
-	// Y-axis: compute tick step and ceiling, then fit within requested height.
-	// Each interval needs at least 2 rows for readable spacing, so
-	// maxIntervals = height/2. If the initial step gives too many intervals,
-	// double it until they fit.
-	tickStep := chartTickStep(maxVal)
-	maxIntervals := height / 2
-	if maxIntervals < 2 {
-		maxIntervals = 2
-	}
-	for {
-		n := int(math.Ceil(maxVal / tickStep))
-		if n <= maxIntervals {
-			break
-		}
-		tickStep *= 2
-	}
-	ceiling := math.Ceil(maxVal/tickStep) * tickStep
-	numIntervals := int(math.Round(ceiling / tickStep))
-	if numIntervals < 1 {
-		numIntervals = 1
-	}
-
-	// Each interval gets the same number of rows; chart height is an exact multiple.
-	rowsPerTick := height / numIntervals
-	if rowsPerTick < 2 {
-		rowsPerTick = 2
-	}
-	chartH := rowsPerTick * numIntervals
-
-	// Pre-compute tick labels at evenly-spaced row positions
-	yLabelW := len(formatChartLabel(ceiling)) + 1
-	if yLabelW < 4 {
-		yLabelW = 4
-	}
-	tickLabels := make(map[int]string)
-	for i := 1; i <= numIntervals; i++ {
-		row := i * rowsPerTick
-		tickLabels[row] = formatChartLabel(tickStep * float64(i))
-	}
-
-	// Chart area width (excluding y-axis label and axis line char)
-	chartW := width - yLabelW - 1
-	if chartW < 5 {
-		chartW = 5
-	}
-
-	n := len(values)
-
-	// Bar sizing: always use 1-char gaps, target barW >= 2.
-	// If bars don't fit at width 2, subsample to fewer bars.
-	gap := 1
-	if n <= 1 {
-		gap = 0
-	}
-	barW := 2
-	if n > 1 {
-		barW = (chartW - (n - 1)) / n
-	} else if n == 1 {
-		barW = chartW
-	}
-	if barW < 2 && n > 1 {
-		// Subsample so bars fit at width 2 with 1-char gaps
-		maxN := (chartW + 1) / 3 // each bar = 2 chars + 1 gap (last bar no gap)
-		if maxN < 2 {
-			maxN = 2
-		}
-		sampled := make([]float64, maxN)
-		var sampledLabels []string
-		if len(labels) == n {
-			sampledLabels = make([]string, maxN)
-		}
-		for i := range sampled {
-			srcIdx := i * (n - 1) / (maxN - 1)
-			sampled[i] = values[srcIdx]
-			if sampledLabels != nil {
-				sampledLabels[i] = labels[srcIdx]
-			}
-		}
-		values = sampled
-		labels = sampledLabels
-		n = maxN
-		barW = 2
-	}
-	if barW > 6 {
-		barW = 6
-	}
-	axisLen := n*barW + max(0, n-1)*gap
-
-	blocks := []rune{' ', '▁', '▂', '▃', '▄', '▅', '▆', '▇', '█'}
-	barStyle := lipgloss.NewStyle().Foreground(color)
-	axisStyle := lipgloss.NewStyle().Foreground(t.TextDim)
-
-	var b strings.Builder
-
-	// Render rows top to bottom using chartH (aligned to tick intervals)
-	for row := chartH; row >= 1; row-- {
-		rowTop := ceiling * float64(row) / float64(chartH)
-		rowBottom := ceiling * float64(row-1) / float64(chartH)
-
-		label := tickLabels[row]
-		b.WriteString(axisStyle.Render(fmt.Sprintf("%*s", yLabelW, label)))
-		b.WriteString(axisStyle.Render("│"))
-
-		for i, v := range values {
-			if i > 0 && gap > 0 {
-				b.WriteString(strings.Repeat(" ", gap))
-			}
-			if v >= rowTop {
-				b.WriteString(barStyle.Render(strings.Repeat("█", barW)))
-			} else if v > rowBottom {
-				frac := (v - rowBottom) / (rowTop - rowBottom)
-				idx := int(frac * 8)
-				if idx > 8 {
-					idx = 8
-				}
-				if idx < 1 {
-					idx = 1
-				}
-				b.WriteString(barStyle.Render(strings.Repeat(string(blocks[idx]), barW)))
-			} else {
-				b.WriteString(strings.Repeat(" ", barW))
-			}
-		}
-		b.WriteString("\n")
-	}
-
-	// X-axis line with 0 label
-	b.WriteString(axisStyle.Render(fmt.Sprintf("%*s", yLabelW, "0")))
-	b.WriteString(axisStyle.Render("└"))
-	b.WriteString(axisStyle.Render(strings.Repeat("─", axisLen)))
-
-	// X-axis labels
-	if len(labels) == n && n > 0 {
-		buf := make([]byte, axisLen)
-		for i := range buf {
-			buf[i] = ' '
-		}
-
-		// Place labels at bar start positions, skip overlaps
-		minSpacing := 8
-		labelStep := max(1, (n*minSpacing)/(axisLen+1))
-
-		lastEnd := -1
-		for i := 0; i < n; i += labelStep {
-			pos := i * (barW + gap)
-			lbl := labels[i]
-			end := pos + len(lbl)
-			if pos <= lastEnd {
-				continue
-			}
-			if end > axisLen {
-				end = axisLen
-				if end-pos < 3 {
-					continue
-				}
-				lbl = lbl[:end-pos]
-			}
-			copy(buf[pos:end], lbl)
-			lastEnd = end + 1
-		}
-		// Always place the last label, right-aligned to axis edge if needed.
-		// Overwrites any truncated label underneath.
-		if n > 1 && len(labels[n-1]) <= axisLen {
-			lbl := labels[n-1]
-			pos := axisLen - len(lbl)
-			end := axisLen
-			// Clear the area first in case a truncated label is there
-			for j := pos; j < end; j++ {
-				buf[j] = ' '
-			}
-			copy(buf[pos:end], lbl)
-		}
-
-		b.WriteString("\n")
-		b.WriteString(strings.Repeat(" ", yLabelW+1))
-		b.WriteString(axisStyle.Render(strings.TrimRight(string(buf), " ")))
-	}
-
-	return b.String()
-}
-
-// chartTickStep computes a nice tick interval targeting ~5 ticks.
-func chartTickStep(maxVal float64) float64 {
-	if maxVal <= 0 {
-		return 1
-	}
-	rough := maxVal / 5
-	exp := math.Floor(math.Log10(rough))
-	base := math.Pow(10, exp)
-	frac := rough / base
-
-	switch {
-	case frac < 1.5:
-		return base
-	case frac < 3.5:
-		return 2 * base
-	default:
-		return 5 * base
-	}
-}
-
-func formatChartLabel(v float64) string {
-	switch {
-	case v >= 1e9:
-		if v == math.Trunc(v/1e9)*1e9 {
-			return fmt.Sprintf("%.0fB", v/1e9)
-		}
-		return fmt.Sprintf("%.1fB", v/1e9)
-	case v >= 1e6:
-		if v == math.Trunc(v/1e6)*1e6 {
-			return fmt.Sprintf("%.0fM", v/1e6)
-		}
-		return fmt.Sprintf("%.1fM", v/1e6)
-	case v >= 1e3:
-		if v == math.Trunc(v/1e3)*1e3 {
-			return fmt.Sprintf("%.0fk", v/1e3)
-		}
-		return fmt.Sprintf("%.1fk", v/1e3)
-	case v >= 1:
-		return fmt.Sprintf("%.0f", v)
-	default:
-		return fmt.Sprintf("%.2f", v)
-	}
-}
-
-// ProgressBar renders a colored progress bar.
-func ProgressBar(pct float64, width int) string {
-	t := theme.Active
-	filled := int(pct * float64(width))
-	if filled > width {
-		filled = width
-	}
-	if filled < 0 {
-		filled = 0
-	}
-
-	filledStyle := lipgloss.NewStyle().Foreground(t.Accent)
-	emptyStyle := lipgloss.NewStyle().Foreground(t.TextDim)
-
-	bar := ""
-	for i := 0; i < filled; i++ {
-		bar += filledStyle.Render("█")
-	}
-	for i := filled; i < width; i++ {
-		bar += emptyStyle.Render("░")
-	}
-
-	return fmt.Sprintf("%s %.1f%%", bar, pct*100)
-}