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

package.json

@@ -15,7 +15,10 @@
   "scripts": {
     "lsp": "tsx ./cli.ts",
     "typecheck": "tsc --noEmit",
-    "lint": "oxlint . --ignore-pattern=.direnv/**"
+    "lint": "oxlint . --ignore-pattern=.direnv/**",
+    "test": "NODE_OPTIONS='--import=tsx' node --test test/unit/**/*.ts test/integration/**/*.ts",
+    "test:unit": "NODE_OPTIONS='--import=tsx' node --test test/unit/**/*.ts",
+    "test:integration": "NODE_OPTIONS='--import=tsx' node --test test/integration/**/*.ts"
   },
   "dependencies": {
     "vscode-jsonrpc": "^8.2.1",