test(mcp): add comprehensive tests + restructure to co-located pattern

Implements Issue #28 - First Adapter + Formatters (Tests)

## Test Coverage

### Formatters (30 tests)
- **formatters.test.ts**: CompactFormatter + VerboseFormatter
  - Single/multiple result formatting
  - Token estimation
  - Empty result handling
  - Signature inclusion/exclusion
  - maxResults option
- **utils.test.ts**: Token estimation utilities
  - Text/JSON token estimation
  - Truncation to token budgets
  - Whitespace normalization
  - Accuracy validation (~50% of actual)

### SearchAdapter (25 tests)
- Tool definition validation
- Query validation (empty, non-string)
- Format validation (compact/verbose/invalid)
- Limit validation (1-50 range)
- Score threshold validation (0-1 range)
- Search execution with mocked indexer
- Token estimation comparison
- Empty result handling

### Restructuring
- ✅ Moved ALL tests from `tests/` to co-located `__tests__/`
- ✅ Updated all import paths (simpler, cleaner)
- ✅ Consistent with `packages/core` and `packages/subagents`
- ✅ Works with root vitest.config.ts out of the box
- ✅ 135 total tests pass (7 test files)

## Benefits
- 🎯 Consistency across entire monorepo
- 📁 Tests co-located with source code
- 🔍 Easier discoverability
- 🚀 Simpler import paths
- ✅ Test discovery works automatically

Author: prosdev

…/tests/adapters/adapter-registry.test.ts …pters/__tests__/adapter-registry.test.tspackages/mcp-server/tests/adapters/adapter-registry.test.ts renamed to packages/mcp-server/src/adapters/__tests__/adapter-registry.test.ts packages/mcp-server/tests/adapters/adapter-registry.test.ts renamed to packages/mcp-server/src/adapters/__tests__/adapter-registry.test.ts

@@ -3,8 +3,8 @@
  */
 
 import { beforeEach, describe, expect, it } from 'vitest';
-import { AdapterRegistry } from '../../src/adapters/adapter-registry';
-import type { AdapterContext } from '../../src/adapters/types';
+import { AdapterRegistry } from '../adapter-registry';
+import type { AdapterContext } from '../types';
 import { MockAdapter } from './mock-adapter';
 
 describe('AdapterRegistry', () => {

…cp-server/tests/adapters/mock-adapter.ts …r/src/adapters/__tests__/mock-adapter.tspackages/mcp-server/tests/adapters/mock-adapter.ts renamed to packages/mcp-server/src/adapters/__tests__/mock-adapter.ts packages/mcp-server/tests/adapters/mock-adapter.ts renamed to packages/mcp-server/src/adapters/__tests__/mock-adapter.ts

@@ -3,14 +3,14 @@
  * Simple echo adapter that returns what you send it
  */
 
-import { ToolAdapter } from '../../src/adapters/tool-adapter';
+import { ToolAdapter } from '../tool-adapter';
 import type {
   AdapterContext,
   ToolDefinition,
   ToolExecutionContext,
   ToolResult,
   ValidationResult,
-} from '../../src/adapters/types';
+} from '../types';
 
 export class MockAdapter extends ToolAdapter {
   readonly metadata = {