chore: add project tooling with Makefile, golangci-lint config, and CLAUDE.md

Establish the quality infrastructure for the cburn project:

- Makefile: standardized targets for build, install, lint, test, test-race,
  bench, and fuzz. Uses explicit Go path (/usr/local/go/bin/go) for
  reproducibility. Fuzz defaults to 30s with FUZZ_TIME override.

- .golangci.yml (v2 format): enables gosec (security), revive (style),
  gocritic (bugs/perf), errcheck, nilerr, perfsprint, prealloc, and
  standard static analysis. Disables noisy rules (exported doc requirement,
  ifElseChain, deferred .Close() gosec G104). Includes gofmt + goimports
  formatters.

- CLAUDE.md: comprehensive project guide covering architecture overview,
  data flow diagram, package map, build/test commands, key design decisions
  (byte-level parsing, mtime-based caching, async TUI loading), and
  configuration reference.

- .gitignore: add pipeline.test to ignored test artifacts.

CLAUDE.md

@@ -0,0 +1,85 @@
+# CLAUDE.md
+
+This file provides guidance to Claude Code (claude.ai/code) when working with code in this repository.
+
+## What This Is
+
+cburn is a CLI + TUI dashboard for analyzing Claude Code usage metrics. It parses JSONL session logs from `~/.claude/projects/`, computes token usage, costs, cache efficiency, and activity patterns, then presents results as CLI tables or an interactive Bubble Tea dashboard.
+
+## Build & Run
+
+A `Makefile` wraps all common commands. Go is at `/usr/local/go/bin/go`.
+
+```bash
+make build          # build ./cburn binary
+make install        # install to ~/go/bin
+
+cburn               # default: summary command
+cburn tui           # interactive dashboard
+cburn costs         # cost breakdown
+cburn --no-cache    # skip SQLite cache, full reparse
+```
+
+## Quality Pipeline
+
+```bash
+make lint           # golangci-lint (config: .golangci.yml)
+make test           # unit tests
+make test-race      # tests with race detector
+make bench          # pipeline benchmarks (uses live ~/.claude data)
+make fuzz           # fuzz the JSONL parser (default 30s, override: FUZZ_TIME=2m)
+```
+
+Lint + test should pass before committing. The linter catches security issues (gosec), unchecked errors (errcheck), performance hints (perfsprint, prealloc), and style (revive).
+
+Tests live alongside the code they test (`*_test.go`). The parser has both unit tests and a fuzz test in `internal/source/parser_test.go`.
+
+## Architecture
+
+### Data Flow
+
+```
+~/.claude/projects/**/*.jsonl
+    -> source.ScanDir() + source.ParseFile()  (parallel, GOMAXPROCS workers)
+    -> store.Cache (SQLite, mtime-based incremental)
+    -> pipeline.Aggregate*() functions
+    -> CLI renderers (cmd/) or TUI tabs (internal/tui/)
+```
+
+### Package Map
+
+| Package | Role |
+|---------|------|
+| `cmd/` | Cobra CLI commands. Each file = one subcommand. `root.go` has shared data loading + filtering. |
+| `internal/source` | File discovery (`ScanDir`) and JSONL parsing (`ParseFile`). Deduplicates by message ID. |
+| `internal/pipeline` | ETL orchestration: parallel loading, cache-aware incremental loading, aggregation functions (`Aggregate`, `AggregateDays`, `AggregateHourly`, `AggregateModels`, `AggregateProjects`). |
+| `internal/store` | SQLite cache layer. Tracks file mtime/size, caches parsed `SessionStats`. |
+| `internal/model` | Domain types: `SessionStats`, `APICall`, `SummaryStats`, `DailyStats`, etc. |
+| `internal/config` | TOML config (`~/.config/cburn/config.toml`), model pricing tables, cost calculation. |
+| `internal/cli` | Terminal formatting: numbers, tokens, costs, tables, horizontal bars. |
+| `internal/claudeai` | claude.ai API client for subscription/usage data. |
+| `internal/tui` | Bubble Tea app. `app.go` is the root model with async data loading. Tab renderers in `tab_*.go`. |
+| `internal/tui/components` | Reusable TUI components: cards, bar charts, sparklines, progress bars, tab bar. |
+| `internal/tui/theme` | Color schemes (flexoki-dark, catppuccin-mocha, tokyo-night, terminal). |
+
+### Key Design Decisions
+
+- **Parsing strategy**: User/system entries use byte-level extraction for speed; only assistant entries get full JSON parse (they carry token/cost data).
+- **Deduplication**: Messages are keyed by message ID; the final state wins (handles edits/retries).
+- **Cache**: SQLite at `~/.cache/cburn/sessions.db`. Mtime+size diffing means unchanged files aren't reparsed.
+- **TUI async loading**: Data loads via goroutines posting `tea.Msg`; the UI remains responsive during parse.
+- **Pricing**: Hardcoded in `internal/config/pricing.go` with user overrides in config TOML. Model names are normalized (date suffixes stripped).
+
+## Configuration
+
+Config file: `~/.config/cburn/config.toml`
+
+Env var fallbacks: `ANTHROPIC_ADMIN_KEY`, `CLAUDE_SESSION_KEY`
+
+Run `cburn setup` for interactive configuration.
+
+## TUI Layout Conventions
+
+- `components.CardInnerWidth(w)` computes usable width inside a card border.
+- `components.LayoutRow(w, n)` splits width into n columns accounting for gaps.
+- When rendering inline bars (like Activity panel), dynamically compute column widths from actual data to prevent line wrapping.