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/dedup.test.ts

@@ -0,0 +1,105 @@
+import { describe, it, expect } from 'vitest';
+import { deduplicateResults } from '../../src/registry/dedup.js';
+import type { RegistryServer } from '../../src/registry/types.js';
+
+function makeServer(overrides: Partial<RegistryServer> = {}): RegistryServer {
+  return {
+    name: 'test-server',
+    description: 'A test server',
+    packages: {},
+    envTemplate: [],
+    transport: 'stdio',
+    popularityScore: 0,
+    verified: false,
+    sourceRegistry: 'official',
+    ...overrides,
+  };
+}
+
+describe('deduplicateResults', () => {
+  it('keeps unique servers', () => {
+    const servers = [
+      makeServer({ name: 'server-a', packages: { npm: 'pkg-a' } }),
+      makeServer({ name: 'server-b', packages: { npm: 'pkg-b' } }),
+    ];
+    expect(deduplicateResults(servers)).toHaveLength(2);
+  });
+
+  it('deduplicates by npm package name, keeps higher popularity', () => {
+    const servers = [
+      makeServer({ name: 'low', packages: { npm: '@test/slack' }, popularityScore: 10, sourceRegistry: 'official' }),
+      makeServer({ name: 'high', packages: { npm: '@test/slack' }, popularityScore: 100, sourceRegistry: 'smithery' }),
+    ];
+    const result = deduplicateResults(servers);
+    expect(result).toHaveLength(1);
+    expect(result[0]?.name).toBe('high');
+    expect(result[0]?.popularityScore).toBe(100);
+  });
+
+  it('deduplicates by GitHub URL with different formats', () => {
+    const servers = [
+      makeServer({ name: 'a', repositoryUrl: 'https://github.com/org/repo', popularityScore: 5 }),
+      makeServer({ name: 'b', repositoryUrl: 'git@github.com:org/repo.git', popularityScore: 50 }),
+    ];
+    const result = deduplicateResults(servers);
+    expect(result).toHaveLength(1);
+    expect(result[0]?.name).toBe('b');
+  });
+
+  it('merges envTemplate from both sources', () => {
+    const servers = [
+      makeServer({
+        name: 'a',
+        packages: { npm: 'pkg' },
+        envTemplate: [{ name: 'TOKEN', description: 'API token', isSecret: true }],
+        popularityScore: 10,
+      }),
+      makeServer({
+        name: 'b',
+        packages: { npm: 'pkg' },
+        envTemplate: [{ name: 'URL', description: 'Base URL', isSecret: false }],
+        popularityScore: 5,
+      }),
+    ];
+    const result = deduplicateResults(servers);
+    expect(result).toHaveLength(1);
+    expect(result[0]?.envTemplate).toHaveLength(2);
+    expect(result[0]?.envTemplate.map((e) => e.name)).toContain('TOKEN');
+    expect(result[0]?.envTemplate.map((e) => e.name)).toContain('URL');
+  });
+
+  it('deduplicates envTemplate by var name', () => {
+    const servers = [
+      makeServer({
+        packages: { npm: 'pkg' },
+        envTemplate: [{ name: 'TOKEN', description: 'from a', isSecret: true }],
+        popularityScore: 10,
+      }),
+      makeServer({
+        packages: { npm: 'pkg' },
+        envTemplate: [{ name: 'TOKEN', description: 'from b', isSecret: true }],
+        popularityScore: 5,
+      }),
+    ];
+    const result = deduplicateResults(servers);
+    expect(result[0]?.envTemplate).toHaveLength(1);
+  });
+
+  it('merges verified status (OR)', () => {
+    const servers = [
+      makeServer({ packages: { npm: 'pkg' }, verified: true, popularityScore: 10 }),
+      makeServer({ packages: { npm: 'pkg' }, verified: false, popularityScore: 5 }),
+    ];
+    const result = deduplicateResults(servers);
+    expect(result[0]?.verified).toBe(true);
+  });
+
+  it('handles servers with no npm or repo', () => {
+    const servers = [
+      makeServer({ name: 'a' }),
+      makeServer({ name: 'b' }),
+    ];
+    // No matching key → no dedup
+    expect(deduplicateResults(servers)).toHaveLength(2);
+  });
+});