test: add unit and integration test suite

Add 34 tests (27 unit, 7 integration) using node:test runner:

Unit tests:
- pickServer(), findRoot(), pathToUri(), uriToPath()
- isLspCommand(), listCommands()
- formatHover(), formatDefinition(), formatReferences(), formatDiagnostics()

Integration tests:
- daemon lifecycle (status/stop) on isolated socket
- CLI --no-daemon queries (hover, documentSymbol, diagnostics)

Supporting changes:
- socketPath() honors PI_LSP_SOCKET_PATH env var for test isolation
- test fixtures for valid and broken TypeScript files
- npm test / test:unit / test:integration scripts

tsconfig.json

@@ -10,5 +10,6 @@
     "noEmit": true,
     "allowImportingTsExtensions": true
   },
-  "include": ["cli.ts", "daemon.ts", "server.ts", "src/**/*.ts"]
+  "include": ["cli.ts", "daemon.ts", "server.ts", "src/**/*.ts", "test/**/*.ts"],
+  "exclude": ["test/fixtures/sample-broken.ts"]
 }