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.

src/init.ts

@@ -1,5 +1,9 @@
 import { discoverProject, type DirectoryEntry } from "./discover.js";
-import { renderPackageMap, type PackageMapData, type FileEntry } from "./format.js";
+import {
+	renderPackageMap,
+	type PackageMapData,
+	type FileEntry,
+} from "./format.js";
 import { extractFileLLM, extractPackageLLM } from "./llm-extract.js";
 import { extractFileAST } from "./ast-extract.js";
 import { mergeFileData } from "./merge.js";