feat: expand MCP tool surface area

[DK09876]

Summary

• Add 18 new MCP tools: directives (list/create/delete), memory browsing (list/get/delete), documents (list/get/delete), operations (list/get/cancel), tags (list), and bank management (get/update/delete/clear_memories/get_bank_stats)
• Expose previously hardcoded parameters on existing tools: retain (tags, metadata, document_id), recall (budget, types, tags, tags_match, query_timestamp), reflect (max_tokens, response_schema, tags, tags_match), create/update_mental_model (trigger_refresh_after_consolidation)
• Update tool registration for both multi-bank (29 tools) and single-bank (26 tools) modes
• Update MCP server docs and local MCP docs with all new tools and parameters

Test plan

• 150 unit tests pass (pytest tests/test_mcp_tools.py tests/test_mcp_extension.py)
• All new tools tested: happy path, error handling, multi-bank and single-bank variants
• New params on existing tools tested with backward compatibility
• Empty list returns, engine errors, and not-found cases covered
• Lint and type checks pass (pre-commit hooks)
• Live end-to-end testing completed against local Hindsight API with Groq provider

Fixes #230