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_audio/package.xml

@@ -0,0 +1,19 @@
+<?xml version="1.0"?>
+<?xml-model href="http://download.ros.org/schema/package_format3.xsd" schematypens="http://www.w3.org/2001/XMLSchema"?>
+<package format="3">
+  <name>hermes_audio</name>
+  <version>0.1.0</version>
+  <description>Microphone and speaker levels, and speaking/listening state, for the Hermes robot.</description>
+  <maintainer email="noreply@example.com">K. Isom</maintainer>
+  <license>UNLICENSED</license>
+
+  <depend>rclpy</depend>
+  <depend>std_msgs</depend>
+  <exec_depend>python3-numpy</exec_depend>
+
+  <test_depend>python3-pytest</test_depend>
+
+  <export>
+    <build_type>ament_python</build_type>
+  </export>
+</package>