feat: Introduce end-to-end MCP protocol tests

[AdrianBesleaga]

Bug Fixes

Module	Bug	Error
server_manager.py	Default server set to non-existent "demo"	Silent failure
resources.py	uid.trim() (Java, not Python)	AttributeError
resources.py	len[adapter] (brackets on builtin)	TypeError
resources.py	Undefined uid in get_document_by_path	NameError
resources.py	Resource handlers returned dict instead of str	Breaks MCP wire protocol
utility.py	ImageContent missing type, mimeType, base64 encoding	ValidationError

Tests Added

• test_regression_fixes.py — 6 unit tests confirming each bug fix
• test_mcp_e2e.py — 6 async tests exercising the real MCP protocol via FastMCP's in-process Client (tool discovery, tool invocation, resource read, prompt/template discovery)

Cleanup

• print() replaced with logger.debug(), removed unused imports, extracted DEFAULT_SERVER_NAME constant
  All 15 new + 70 existing unit tests pass.