Add self-extension tool system: write_tool, list_tools, tool_manual ...

- loader.py: module-level format (name/description/parameters/execute)
  preferred, class-based as fallback; isolated errors per file
- write_tool: validates + writes tools/name.py, reloads registry,
  adds to tools/enabled.json in one call
- list_tools: live tool list from registry (prevents hallucination)
- tool_manual: serves manuals/*.md or auto-generates from schema
- reload_tools: hot-reload without server restart
- registry: registry injection pattern for tools that need it;
  _builtin_names set to guard against reload overwriting builtins

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

Add multimodal image support and client UX improvements ...

Server:
- Add ImageViewTool (load image from file/URL, returns base64)
- Add images field to Message model with created_at timestamp
- Agent run/run_stream accept images param; inject image messages after image_view tool calls
- WebSocket handler accepts images array from client, strips data URI prefix
- All profiles include image_view tool
- Fix tool call serialization (model_dump mode=json for datetime)
- Add no-store cache headers for static files

Client:
- Image attachment: file picker button + clipboard paste + preview strip with remove
- Images rendered in chat bubbles; loaded from history
- Tool cards rebuilt as div+CSS toggle (fixes details/overflow-hidden collapse bug)
- Tool cards appear before response bubble (lazy bubble creation on first stream_delta)
- Typing indicator persists through tool calls, removed only when text starts streaming
- Tool cards restored from history on page reload
- Message timestamps stored via created_at field, shown correctly in history
- Session ID reflected in URL hash for bookmarking; restored on page load
- Remove localStorage session tracking (server last_active used instead)

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

ssh_exec: accept credentials directly as tool parameters ...

host, username, password, port, key_path are now first-class parameters.
No config file needed — user can pass creds in the chat message.
Ad-hoc connections skip host key verification by default.
Named connections in ssh_hosts.json still work as a shortcut.

Fix SSH password auth: disable key lookup when password is configured ...

asyncssh tried ~/.ssh/* keys before the password, causing PermissionDenied
on hosts that only accept password auth. Now when 'password' is set and no
'client_keys', key auth is disabled entirely.

Filesystem tool: unrestricted mode by default ...

FS_ALLOWED_PATHS=* (default) allows any path, consistent with terminal.
Path check is now lazy (per-request) instead of module-level,
so config is always fresh after restart.
~ expansion added.

Unrestricted terminal mode and SSH tool ...

- Terminal: TERMINAL_ALLOWED_COMMANDS=* (default) runs via shell,
  supports pipes, redirects, subshells; allowlist mode still available
- FS_ALLOWED_PATHS expanded to cover /home /etc /var /opt
- New ssh_exec tool: execute commands on remote hosts via asyncssh,
  supports named connections (ssh_hosts.json) and inline user@host
- ssh_hosts.json gitignored, ssh_hosts.json.example added as reference
- ssh_exec added to server_admin and smart_home profiles

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