Integration tests: MCP STDIO end-to-end with temp DB

[BrainSlugs83]

Description

Add integration tests that exercise the full MCP STDIO pipeline end-to-end:
spawn the proxy (index.js) via a PTY, send JSON-RPC messages, and validate responses.

Requirements

1. Temp DB isolation — Add VECTOR_MEMORY_DATA_DIR env var override to
   vector-memory-server.js so tests can point at a temp directory instead
   of ~/.copilot/. Delete the temp dir after tests.

2. PTY wrapper — Use node-pty (or similar) to spawn index.js and
   interact via MCP JSON-RPC over stdin/stdout.

3. Test cases (positive + negative):

   • vector_search with a valid query → returns results array
   • vector_search with missing query param → returns error
   • vector_reindex → returns count
   • tools/list → lists both tools with correct schemas
   • Initialize handshake completes successfully

4. Cleanup — Temp DB directory is removed after test run.

Notes

• The three HTTP endpoints on the server are /ping, /search, /reindex
• The proxy forwards MCP tool calls to the HTTP server via callServerWithRetry()
• DB paths are currently hardcoded in vector-memory-server.js:17-19

[BrainSlugs83]

Resolved by PR #3 — integration tests added in test-integration.js covering MCP STDIO e2e pipeline with temp DB isolation.