Bump version to 0.99.57; add Claude CLI proxy mode

- Add aisbf/cli_mode.py: detect claude binary in PATH at startup
- Add ClaudeCliSessionManager: per-user isolated temp config dirs with
  10-minute idle cleanup and asyncio subprocess-based request proxying
- Add ClaudeProviderHandler CLI methods: _get_cli_credentials,
  _messages_to_cli_prompt, _handle_cli_streaming_request,
  _handle_cli_request, _oauth_tokens_to_cli_credentials
- Wire CLI mode check into _handle_request_with_model; falls through to
  HTTP API mode when no CLI credentials are configured
- Add 'Use Claude CLI mode' checkbox in provider config (both admin and
  user templates): derives credentials from existing OAuth2 tokens
- Add explicit CLI credentials file upload (file_type=cli_credentials);
  DB users: stored in user_oauth2_credentials; admin: path in providers.json
- Update Claude provider warning notices to scope risk to HTTP API mode
  and clarify that claude -p is permitted by Claude's terms of service
- Update CHANGELOG.md, DOCUMENTATION.md, README.md