feat: gstack dashboard — UX visualizer for sprint pipeline & analytics

[HMAKT99]

Summary

• New dashboard/ module — self-contained Bun HTTP server + single-page app that visualizes all gstack data sources in a dark/light themed web dashboard
• 8 dashboard views: Overview (metrics + pipeline), Sprint Pipeline, QA Reports (health rings + severity breakdown), Performance (Core Web Vitals gauges), Canary Monitor (alerts + page health), Design Review (radar chart + scores), Analytics (usage/success/duration charts), Browser Sessions (console/network/dialog logs), Eureka Log
• 14 JSON API endpoints reading from .gstack/ reports, ~/.gstack/analytics/, browse daemon state, and git info
• Dark + Light theme with toggle button, localStorage persistence, and theme-aware SVG charts
• Stage Mode (/?mode=stage) — projector-optimized presentation view for live gstack demos with animated pipeline, big counter metrics, live activity feed, elapsed clock, and 5-second polling
• Zero dependencies — vanilla HTML/CSS/JS, SVG-based charts, follows the cookie-picker-ui.ts self-contained pattern
• Launch with bun run dashboard

Stage Mode

Presentation view built for projecting gstack during live demos and meetups:

• Full-screen layout — no sidebar, no chrome, just content
• Giant animated sprint pipeline with pulse/glow effects on active stages
• 56px counter wall: Skill Runs, Success Rate, Reports, Eureka Moments
• Live activity feed with slide-in animations
• Top skills chart with color-coded bars
• Elapsed time clock (MM:SS)
• 5-second polling (6x faster than normal mode)
• Access: bun run dashboard → /?mode=stage or click "Stage" button

Files changed

File	Lines	Purpose
dashboard/data.ts	464	Data access layer — reads all .gstack/ and ~/.gstack/ data sources
dashboard/server.ts	157	Bun HTTP server with 14 API routes + HTML serving
dashboard/ui.ts	2177	Complete SPA — HTML/CSS/JS with dark/light themes, SVG charts, stage mode
package.json	+1	Added dashboard script

Test plan

• Run bun run dashboard — verify server starts and prints URL
• Open dashboard in browser — verify Overview loads with metrics and pipeline
• Click through all 8 views — verify each renders correctly
• Toggle dark/light theme — verify all views update including SVG charts
• Refresh page — verify theme preference persists
• Navigate to /?mode=stage — verify stage mode renders with pipeline, metrics, feed
• Verify stage mode elapsed clock ticks
• Verify stage mode polls every 5 seconds (check Network tab)
• Test with no data (empty .gstack/) — verify empty states show gracefully
• Test with sample data in .gstack/qa-reports/, benchmark-reports/, etc.
• Verify bun test still passes (no existing tests affected)

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