Wire self-extension tools into all profiles; improve tool descriptions ...

All profiles now include write_tool, list_tools, tool_manual, reload_tools.
User tools from enabled.json merged in at runtime via Agent._tool_list().
Built-in tool descriptions rewritten to be more LLM-actionable.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Initial implementation of the agent system core ...

- FastAPI server with REST API and WebSocket streaming
- Modular LLM backend abstraction (Ollama implemented, OpenAI stub)
- Tool system: web_search (ddgs), filesystem, http_request, code_exec, terminal
- Agent profiles: smart_home, server_admin, secretary
- Tool-calling loop with concurrent tool execution
- In-memory session store with SessionStore ABC for future persistence
- Registry pattern for tools, profiles, and backends
- Orchestrator stub as foundation for multi-agent scenarios