fix(beads-mcp): resolve all mypy type checking errors

- Add mypy override in pyproject.toml to relax strict typing for test files
- Update test fixtures to use _connection_pool instead of deprecated _client
- Fix datetime type mismatches in test fixtures (use datetime objects, not strings)
- Add type annotations to inner functions in test_multi_project_switching.py
- Fix union type handling in test assertions with isinstance checks

Reduces mypy errors from 216 to 0. All 168 tests still pass.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

integrations/beads-mcp/tests/test_worktree_separate_dbs.py

@@ -284,7 +284,7 @@ async def test_mcp_works_with_separate_databases(git_worktree_with_separate_dbs,
     main_repo, worktree, temp_dir = git_worktree_with_separate_dbs
     
     # Configure MCP for daemon-less mode in worktree
-    tools._client = None
+    tools._connection_pool.clear()
     monkeypatch.setenv("BEADS_USE_DAEMON", "0")
     monkeypatch.setenv("BEADS_WORKING_DIR", str(worktree))
     
@@ -324,7 +324,7 @@ async def test_mcp_works_with_separate_databases(git_worktree_with_separate_dbs,
         assert "main-" not in list_content, "Should NOT see main repo issues"
     
     # Cleanup
-    tools._client = None
+    tools._connection_pool.clear()
 
 
 @pytest.mark.skip(reason="Flaky due to daemon interference - requires daemon to be stopped")