feat: persistent Gemini ACP provider + status spinner

Replace per-call gemini CLI spawning (~10s cold start each time) with
persistent ACP (Agent Client Protocol) subprocess. First call absorbs
the cold start, subsequent calls are near-instant over JSON-RPC stdio.

- Add AcpClient: manages persistent gemini --experimental-acp subprocess
  with lazy init, auto-restart on crash/timeout, NDJSON framing
- Add GeminiAcpProvider: LlmProvider wrapper with serial queue for
  concurrent calls, same interface as GeminiCliProvider
- Add dispose() to LlmProvider interface + disposeAll() to registry
- Wire provider disposal into mcplocal shutdown handler
- Add status command spinner with progressive output and color-coded
  LLM health check results (green checkmark/red cross)
- 25 new tests (17 ACP client + 8 provider)

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/mcplocal/tests/llm-config.test.ts

@@ -25,7 +25,7 @@ describe('createProviderFromConfig', () => {
     expect(registry.getActive()).toBeNull();
   });
 
-  it('creates gemini-cli provider', async () => {
+  it('creates gemini-cli provider using ACP', async () => {
     const store = mockSecretStore();
     const registry = await createProviderFromConfig(
       { provider: 'gemini-cli', model: 'gemini-2.5-flash', binaryPath: '/usr/bin/gemini' },
@@ -33,6 +33,8 @@ describe('createProviderFromConfig', () => {
     );
     expect(registry.getActive()).not.toBeNull();
     expect(registry.getActive()!.name).toBe('gemini-cli');
+    // ACP provider has dispose method
+    expect(typeof registry.getActive()!.dispose).toBe('function');
   });
 
   it('creates ollama provider', async () => {