audio: delete dead local wobbler module and clean up unused state

Removes everything that exists only to support the in-process speech
tapper that the daemon now replaces:

  - Delete src/reachy_mini_conversation_app/audio/{head_wobbler.py,
    speech_tapper.py,__init__.py} and the now-empty audio/ package.
  - Delete tests/audio/test_head_wobbler.py and the audio/ test dir.
  - Drop head_wobbler: Any | None = None from ToolDependencies.
  - In MovementManager, drop set_speech_offsets() and the supporting
    state (state.speech_offsets, _pending_speech_offsets,
    _speech_offsets_lock, _speech_offsets_dirty, the speech-side of
    _apply_pending_offsets, the speech term in _get_secondary_pose).
    Speech-induced offsets are now produced by the daemon's wobbler
    and composed server-side via SetSpeechOffsetsCmd, so the local
    composition path is no longer needed.

Updates the only remaining test that mocked head_wobbler:
test_gemini_turn_buffers_transcripts (was
test_gemini_turn_buffers_transcripts_and_schedules_motion_reset).
Drops the wobbler mock and assertions, keeps the transcript and
listening-state assertions which still describe real behaviour, and
swaps the wait-for predicate to use output_queue size and listening
call count instead of wobbler interaction.

Author: RemiFabre