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

test/unit/commands.test.ts

@@ -0,0 +1,34 @@
+// Commands Unit Tests — isLspCommand(), listCommands().
+import { describe, it } from "node:test";
+import * as assert from "node:assert/strict";
+import { isLspCommand, listCommands } from "../../src/commands.ts";
+
+describe("listCommands", () => {
+  it("returns all known commands", () => {
+    const cmds = listCommands();
+    assert.ok(Array.isArray(cmds));
+    assert.ok(cmds.includes("hover"));
+    assert.ok(cmds.includes("definition"));
+    assert.ok(cmds.includes("references"));
+    assert.ok(cmds.includes("completion"));
+    assert.ok(cmds.includes("documentSymbol"));
+    assert.ok(cmds.includes("diagnostics"));
+  });
+});
+
+describe("isLspCommand", () => {
+  it("returns true for known commands", () => {
+    assert.strictEqual(isLspCommand("hover"), true);
+    assert.strictEqual(isLspCommand("definition"), true);
+    assert.strictEqual(isLspCommand("references"), true);
+    assert.strictEqual(isLspCommand("completion"), true);
+    assert.strictEqual(isLspCommand("documentSymbol"), true);
+    assert.strictEqual(isLspCommand("diagnostics"), true);
+  });
+
+  it("returns false for unknown strings", () => {
+    assert.strictEqual(isLspCommand("format"), false);
+    assert.strictEqual(isLspCommand(""), false);
+    assert.strictEqual(isLspCommand("hover "), false);
+  });
+});