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.

package.json

@@ -25,15 +25,16 @@
   "license": "MIT",
   "devDependencies": {
     "@types/node": "^20.0.0",
-    "typescript": "^5.3.0",
-    "vitest": "^1.0.0",
-    "eslint": "^8.0.0",
     "@typescript-eslint/eslint-plugin": "^6.0.0",
-    "@typescript-eslint/parser": "^6.0.0"
+    "@typescript-eslint/parser": "^6.0.0",
+    "eslint": "^8.0.0",
+    "tsx": "^4.22.4",
+    "typescript": "^5.3.0",
+    "vitest": "^1.0.0"
   },
   "dependencies": {
+    "ignore": "^5.3.0",
     "tree-sitter": "^0.21.0",
-    "tree-sitter-typescript": "^0.21.0",
-    "ignore": "^5.3.0"
+    "tree-sitter-typescript": "^0.21.0"
   }
 }