feat: make session name generation configurable

[itsmariush]

Summary

Makes session auto-naming configurable via TUI settings (tui.json) and CLI flag (--auto-name-session/--no-auto-name-session). When auto-naming is disabled, the session falls back to a simple 4-word title derived from the first user message.

Why

Improve session start up time. Especially when using local reasoning models this saves up to 45s.

Changes

• TUI config: Added auto_name_session: bool = True to TuiSettings (defaults to enabled)

• CLI flag: Added --auto-name-session/--no-auto-name-session option for print mode (defaults to disabled)

• Session config: Added auto_name_session parameter through CodingSessionConfig → CodingSession

• Fallback naming: When auto-generation is disabled, uses _fallback_session_name() (first 4 words of prompt) instead of skipping naming entirely

• Print mode defaults: Print mode defaults to auto_name_session=False to avoid unnecessary API calls in non-interactive mode
  ## Files Changed

• src/tau_coding/cli.py — CLI flag + parameter wiring

• src/tau_coding/session.py — Config field + fallback logic in _try_auto_name_session

• src/tau_coding/tui/app.py — TUI settings wiring

• src/tau_coding/tui/config.py — TuiSettings field + JSON serialization

Testing

• All 5 existing auto_name tests pass
• TUI config tests pass
• One pre-existing unrelated test failure (test_load_empty_session_defers_transcript_file)

Related

Addresses the need for users to disable auto session naming in print mode and control the behavior per-project via tui.json.