feat(viewer): group-by-project toggle + Gitea 404 handling

- static/board.js: full rerender on toggle-grouping; by-project mode = N cols
  per project with status-badge inside cards, sorted by canonical status order
- static/board.css: drop placeholder, add .badge.status
- src/gitea.ts: getLatestCommitIso returns null on 404 (path never existed
  remotely; seen on books repo where some per-task slugs in STATUS.md
  don't have file in default branch) + new test
- .gitignore: dist/ already present; add .playwright-mcp/, board-*.png

Smoke-verified: dist/index.html, 78 records from 4 repos, both toggle modes
work in browser, drawer lazy-fetches markdown.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

.gitignore

@@ -9,6 +9,11 @@ dist/
 build/
 *.egg-info/
 
+# Playwright MCP scratch
+.playwright-mcp/
+board-viewer-*.png
+board-by-project.png
+
 # Environment
 .env
 .env.local