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/fixtures/sample-broken.ts

@@ -0,0 +1,12 @@
+// Broken Fixture — Intentional type errors for diagnostics testing.
+
+/** This variable has a type mismatch — string assigned to number. */
+export const brokenNumber: number = "not a number";
+
+/** This function returns wrong type — string instead of boolean. */
+export function brokenBoolean(): boolean {
+  return "yes";
+}
+
+/** This variable uses an undefined identifier. */
+export const brokenReference = definitelyUndefined;

test/fixtures/sample.ts

@@ -0,0 +1,38 @@
+// Sample Fixture — Minimal TypeScript file with known symbols for LSP testing.
+// Used by integration tests to validate hover, definition, references, etc.
+
+/**
+ * A sample class for testing LSP features.
+ * @example new SampleClass("hello")
+ */
+export class SampleClass {
+  public readonly name: string;
+
+  constructor(name: string) {
+    this.name = name;
+  }
+
+  /** Returns a greeting using the instance name. */
+  greet(): string {
+    return `Hello, ${this.name}!`;
+  }
+}
+
+/** A constant value for reference testing. */
+export const SAMPLE_CONSTANT = 42;
+
+/** Creates a new SampleClass with a default name. */
+export function createSample(): SampleClass {
+  return new SampleClass("default");
+}
+
+// Internal helper — not exported, used to test definition lookups.
+function internalHelper(value: number): string {
+  return String(value);
+}
+
+/** Uses the internal helper and constant for cross-reference testing. */
+export function useInternal(): string {
+  const instance = createSample();
+  return internalHelper(SAMPLE_CONSTANT) + instance.greet();
+}