Restructure profiles: directory-based format with config.json + system_prompt.txt ...

Each profile is now a subdirectory under navi/profiles/ containing:
  config.json       — model, temperature, enabled_tools, and other settings
  system_prompt.txt — raw system prompt, editable without touching Python

Added navi/profiles/loader.py for auto-discovery of profile directories.
Removed individual profile .py files (secretary, server_admin, smart_home, developer).
profiles/__init__.py now simply calls load_profiles_from_dir() at import time.

New profiles can be added by creating a directory with the two required files —
no Python changes needed.

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

Add developer profile; replace write_tool pattern with direct filesystem approach ...

- New TestToolTool: runs a user tool's execute() from disk in isolation,
  returns result or full traceback. No stale module cache — always fresh import.
- New developer profile: full architecture knowledge in system prompt
  (format rules, file locations, workflow, data persistence, common mistakes),
  test_tool + reload_tools + filesystem/terminal/code_exec toolset, spawn_agent
  for API research only.
- Remove write_tool and reload_tools from server_admin and smart_home profiles.
- persona.txt: drop SELF-EXTENSION block; add one-liner to switch to developer
  profile when the user asks to create/edit a tool.

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