feat: implement MCP registry client with multi-source search

Add registry client that queries Official, Glama, and Smithery MCP
registries with caching, request deduplication, retry logic, and
result ranking/dedup. Includes 53 tests covering all components.

Also fix null priority values in cancelled tasks (19-21) that broke
Task Master, and add new tasks 25-27 for registry completion and
CLI discover/install commands.

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

src/cli/tests/registry/cache.test.ts

@@ -0,0 +1,90 @@
+import { describe, it, expect, vi, beforeEach, afterEach } from 'vitest';
+import { RegistryCache } from '../../src/registry/cache.js';
+import type { RegistryServer, SearchOptions } from '../../src/registry/types.js';
+
+function makeServer(name: string): RegistryServer {
+  return {
+    name,
+    description: `${name} server`,
+    packages: {},
+    envTemplate: [],
+    transport: 'stdio',
+    popularityScore: 0,
+    verified: false,
+    sourceRegistry: 'official',
+  };
+}
+
+const defaultOptions: SearchOptions = { query: 'test' };
+
+describe('RegistryCache', () => {
+  beforeEach(() => {
+    vi.useFakeTimers();
+  });
+  afterEach(() => {
+    vi.useRealTimers();
+  });
+
+  it('returns null for cache miss', () => {
+    const cache = new RegistryCache();
+    expect(cache.get('unknown', defaultOptions)).toBeNull();
+  });
+
+  it('returns data for cache hit within TTL', () => {
+    const cache = new RegistryCache();
+    const data = [makeServer('test')];
+    cache.set('test', defaultOptions, data);
+    expect(cache.get('test', defaultOptions)).toEqual(data);
+  });
+
+  it('returns null after TTL expires', () => {
+    const cache = new RegistryCache(1000); // 1 second TTL
+    cache.set('test', defaultOptions, [makeServer('test')]);
+
+    vi.advanceTimersByTime(1001);
+    expect(cache.get('test', defaultOptions)).toBeNull();
+  });
+
+  it('generates deterministic cache keys', () => {
+    const cache = new RegistryCache();
+    const data = [makeServer('test')];
+    cache.set('query', { query: 'query', limit: 10 }, data);
+    expect(cache.get('query', { query: 'query', limit: 10 })).toEqual(data);
+  });
+
+  it('generates different keys for different queries', () => {
+    const cache = new RegistryCache();
+    cache.set('a', { query: 'a' }, [makeServer('a')]);
+    expect(cache.get('b', { query: 'b' })).toBeNull();
+  });
+
+  it('tracks hits and misses correctly', () => {
+    const cache = new RegistryCache();
+    cache.set('test', defaultOptions, [makeServer('test')]);
+
+    cache.get('test', defaultOptions); // hit
+    cache.get('test', defaultOptions); // hit
+    cache.get('miss', { query: 'miss' }); // miss
+
+    const ratio = cache.getHitRatio();
+    expect(ratio.hits).toBe(2);
+    expect(ratio.misses).toBe(1);
+    expect(ratio.ratio).toBeCloseTo(2 / 3);
+  });
+
+  it('returns 0 ratio when no accesses', () => {
+    const cache = new RegistryCache();
+    expect(cache.getHitRatio().ratio).toBe(0);
+  });
+
+  it('clears all entries and resets metrics', () => {
+    const cache = new RegistryCache();
+    cache.set('a', { query: 'a' }, [makeServer('a')]);
+    cache.get('a', { query: 'a' }); // hit
+    cache.clear();
+
+    expect(cache.get('a', { query: 'a' })).toBeNull();
+    expect(cache.size).toBe(0);
+    expect(cache.getHitRatio().hits).toBe(0);
+  });
+});