feat: add TUI auto-refresh with configurable interval and manual refresh

Introduce background data refresh so the dashboard stays current without
restarting. This touches four layers:

Config (config.go):
- New TUIConfig struct with AutoRefresh (bool) and RefreshIntervalSec
  (int) fields, defaulting to enabled at 30-second intervals.
- Minimum interval floor of 10 seconds enforced at load time.

App core (app.go):
- RefreshDataMsg type for background refresh completion signaling.
- Auto-refresh state: interval timer, refreshing flag, lastRefresh
  timestamp. Checked on every tick; fires refreshDataCmd when elapsed.
- refreshDataCmd: background goroutine that loads session data via cache
  (with uncached fallback) and posts RefreshDataMsg on completion.
- Manual refresh keybind: 'r' triggers immediate refresh.
- Auto-refresh toggle keybind: 'R' toggles auto-refresh and persists
  the preference to config.toml.
- Help text updated with r/R keybind documentation.

Status bar (statusbar.go):
- Shows spinning refresh indicator during active refresh.
- Shows auto-refresh icon when auto-refresh is enabled.

Settings tab (tab_settings.go):
- Two new editable fields: Auto Refresh (bool) and Refresh Interval
  (seconds with 10s minimum).
- Settings display reads live App state to stay consistent with the
  R toggle keybind (avoids stale config-file reads).

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

internal/tui/components/statusbar.go

@@ -12,21 +12,29 @@ import (
 )
 
 // RenderStatusBar renders the bottom status bar with optional rate limit indicators.
-func RenderStatusBar(width int, dataAge string, subData *claudeai.SubscriptionData) string {
+func RenderStatusBar(width int, dataAge string, subData *claudeai.SubscriptionData, refreshing, autoRefresh bool) string {
 	t := theme.Active
 
 	style := lipgloss.NewStyle().
 		Foreground(t.TextMuted).
 		Width(width)
 
-	left := " [?]help  [q]uit"
+	left := " [?]help  [r]efresh  [q]uit"
 
 	// Build rate limit indicators for the middle section
 	ratePart := renderStatusRateLimits(subData)
 
-	right := ""
-	if dataAge != "" {
-		right = fmt.Sprintf("Data: %s ", dataAge)
+	// Build right side with refresh status
+	var right string
+	if refreshing {
+		refreshStyle := lipgloss.NewStyle().Foreground(t.Accent)
+		right = refreshStyle.Render("↻ refreshing ")
+	} else if dataAge != "" {
+		autoStr := ""
+		if autoRefresh {
+			autoStr = "↻ "
+		}
+		right = fmt.Sprintf("%sData: %s ", autoStr, dataAge)
 	}
 
 	// Layout: left + ratePart + right, with padding distributed