Fix discover, improve LLM heuristics, add integration tests

- discover.ts: Fix ignore package path handling for root '.' directories,
  add .pi-map.md to default ignore list
- llm-extract.ts: Fix export regex to only match line-start exports and
  handle 'export async function', fix root package role to 'Project root'
- init.ts: Minor cleanup
- .gitignore: Add .pi-map.md
- tests: 6 integration tests covering init, patch (small/large packages),
  validate (missing, orphaned, stale-signature detection)

All 14 tests pass. TypeScript compiles clean.

.gitignore

@@ -4,3 +4,4 @@ coverage/
 *.log
 .DS_Store
 .env
+.pi-map.md