Add hermes_audio and draw the mouth from the real waveform

audio_state taps the microphone and the speaker monitor with parec and publishes
levels, a speaking/listening/quiet activity, and trigger-locked waveform windows;
audio itself stays out of ROS. The activity detector calibrates its noise floor
at start-up and absorbs steady noise, so a room at -43 dBFS does not read as
"listening" forever, and it ignores the mic while the robot speaks.

The face arbitrates the state it shows: sleeping (agent side only, so room sound
never wakes a face that means "no agent connected") > speaking > listening >
thinking > idle, and draws the mouth from the real samples while fresh scope data
exists, auto-scaled so a quiet voice is still visible.

Checked: a tone played to the sink shows as `speaking` with the mic ignored. The
microphone-to-mouth path with a live voice is not yet confirmed.

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01AFN8nRRCiDiMN7ChBpHJhs

ros/hermes_face/test/test_arbiter.py

@@ -0,0 +1,20 @@
+import pytest
+
+from hermes_face.arbiter import resolve_state
+
+
+@pytest.mark.parametrize('agent,audio,expected', [
+    ('sleeping', 'quiet', 'sleeping'),
+    ('sleeping', 'listening', 'sleeping'),       # room sound never wakes the face
+    ('sleeping', 'speaking', 'sleeping'),
+    ('idle', 'quiet', 'idle'),
+    ('idle', 'listening', 'listening'),
+    ('idle', 'speaking', 'speaking'),
+    ('thinking', 'quiet', 'thinking'),
+    ('thinking', 'listening', 'listening'),      # a voice interrupts the thinking face
+    ('listening', 'quiet', 'listening'),
+    ('speaking', 'quiet', 'speaking'),           # the agent says it is speaking before the audio shows it
+    ('thinking', 'speaking', 'speaking'),
+])
+def test_priority(agent, audio, expected):
+    assert resolve_state(agent, audio) == expected