Add hermes_vision, build camera_ros on the fork, and bring up WM8960 audio

hermes_vision wraps OpenCV YuNet (Haar fallback) as a plain module plus a node
that publishes /vision/faces as vision_msgs/Detection2DArray. It replaces the
standalone detect_faces.py. pi/robot-env.sh puts the Raspberry Pi libcamera fork
ahead of ROS's own copy, the venv's OpenCV 4.10 ahead of the apt one, and fixes
the ROS domain and subnet-only discovery. camera_ros 0.7.0 now runs against the
fork and publishes raw and compressed images.

The stock wm8960-soundcard overlay fails on Ubuntu 24.04 with "No MCLK
configured": it hangs the clock on the sound card's codec link, but the codec
driver reads mclk from its own node. hermes-wm8960.dts adds it there, and
capture opens at 8-48 kHz. The microphones still read digital zeros; see
CONTEXT.md for what has been ruled out.

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

ros/hermes_vision/test/test_detect.py

@@ -0,0 +1,27 @@
+import numpy as np
+import pytest
+
+from hermes_vision.detect import Face, FaceDetector, merge, yunet_input_size
+
+
+@pytest.mark.parametrize('size,expected', [
+    ((1296, 972), (640, 480)),
+    ((640, 480), (640, 480)),
+    ((320, 240), (320, 256)),     # small frames are not upscaled; 240/32 = 7.5 rounds to 8
+    ((1920, 1080), (640, 352)),
+    ((10, 10), (32, 32)),
+])
+def test_yunet_input_size_is_a_multiple_of_32(size, expected):
+    got = yunet_input_size(*size)
+    assert got == expected and got[0] % 32 == 0 and got[1] % 32 == 0
+
+
+def test_merge_drops_overlapping_boxes_and_keeps_distinct_ones():
+    a, b, c = Face(100, 100, 80, 80), Face(105, 98, 78, 82), Face(400, 100, 80, 80)
+    assert merge([a, b, c]) == [a, c]
+
+
+def test_blank_image_has_no_faces():
+    det = FaceDetector(model_path='/nonexistent.onnx')      # forces the Haar fallback
+    assert det.backend == 'haar'
+    assert det.detect(np.zeros((480, 640, 3), np.uint8)) == []