Implement all stubs: parsePackageMap, LLM heuristics, tree-sitter AST, patch rewrite, reinit

- format.ts: Full parsePackageMap implementation with round-trip support
- llm-extract.ts: Heuristic-based extraction without LLM API (regex exports,
  imports, purpose inference from filename patterns)
- ast-extract.ts: Tree-sitter integration for TypeScript/TSX with fallback
  for other languages
- init.ts: Refactored to expose generateDirectoryMap helper, reinitPath
  delegates to initProject
- patch.ts: Small packages now use generateDirectoryMap for full rewrite
- discover.ts: Cleaned up require('fs') to use proper ES import
- Tests: 8 tests covering format round-trip and LLM heuristics
- All TypeScript compiles clean, all tests pass

src/index.ts

@@ -1,5 +1,5 @@
 // Main entry point for pi-project-map skill
-export { initProject } from './init.js';
-export { patchFile } from './patch.js';
-export { validateMaps } from './validate.js';
-export { renderPackageMap, parsePackageMap } from './format.js';
+export { initProject } from "./init.js";
+export { patchFile } from "./patch.js";
+export { validateMaps } from "./validate.js";
+export { renderPackageMap, parsePackageMap } from "./format.js";