Add hermes_face ROS package and verify the display on the Pi

The Pi (hermes-bot) is flashed, upgraded and running ROS 2 Jazzy. The ST7789
works through Blinka on lgpio: pass cs=None (the kernel owns CE0), and the glass
sits at y_offset=80 in the controller RAM for every rotation, since the driver
rotates in software. The mounted pose needs rotation=270.

hermes_face is a numpy port of the flat face from docs/face-prototype.html, with
phosphor and vector styles, plus a new `sleeping` pose for "no agent connected".
The renderer has no ROS or hardware imports. The tone map is a lookup table and
the glow runs at half resolution, so the face reaches ~28 fps on the panel at
24% of a core (20 fps) to 40% (30 fps) with the CPU at full clock.

CONTEXT.md now records the Pi, the cloud-init first-boot-only gotcha, and what
is left. pi/50-cloud-init.yaml is a gitignored Wi-Fi template.

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

ros/hermes_face/test/test_render.py

@@ -0,0 +1,101 @@
+import numpy as np
+import pytest
+
+from hermes_face.render import H, STATES, W, FaceRenderer, box_blur
+
+
+def run(r, seconds, t0=0.0, fps=30):
+    t, frame = t0, None
+    for _ in range(int(seconds * fps)):
+        t += 1 / fps
+        frame = r.frame(t, 1 / fps)
+    return frame, t
+
+
+def brightness(frame):
+    return float(frame.astype(np.float32).mean())
+
+
+@pytest.mark.parametrize('state', STATES)
+@pytest.mark.parametrize('style', ['phosphor', 'vector'])
+def test_every_state_draws_something(state, style):
+    frame, _ = run(FaceRenderer(style=style, state=state, seed=0), 3)
+    assert frame.shape == (H, W, 3) and frame.dtype == np.uint8
+    assert frame.max() > 100
+
+
+def test_sleeping_is_dimmer_than_idle():
+    idle, _ = run(FaceRenderer(state='idle', seed=0), 4)
+    asleep, _ = run(FaceRenderer(state='sleeping', seed=0), 4)
+    assert brightness(asleep) < 0.8 * brightness(idle)
+
+
+def test_wakes_up():
+    r = FaceRenderer(state='sleeping', seed=0)
+    _, t = run(r, 2)
+    r.set_state('idle', t)
+    frame, _ = run(r, 3, t)
+    idle, _ = run(FaceRenderer(state='idle', seed=0), 3)
+    assert r.a['open'] > 0.9 and abs(brightness(frame) - brightness(idle)) < 0.2 * brightness(idle)
+
+
+def test_looking_returns_to_the_state_it_interrupted():
+    r = FaceRenderer(state='thinking', seed=0)
+    _, t = run(r, 1)
+    r.set_state('looking', t)
+    assert r.state == 'looking'
+    run(r, 2, t)
+    assert r.state == 'thinking'
+
+
+def test_unknown_state_rejected():
+    with pytest.raises(ValueError):
+        FaceRenderer().set_state('dancing', 0.0)
+
+
+def test_pan_moves_the_eyes():
+    def centroid_x(pan):
+        r = FaceRenderer(state='idle', seed=0, jitter=0)
+        r.set_pose(pan, 0)
+        frame, _ = run(r, 2)
+        lum = frame.astype(np.float32).sum(axis=(0, 2))
+        return float((lum * np.arange(W)).sum() / lum.sum())
+    assert centroid_x(-60) > centroid_x(0) > centroid_x(60)   # +pan = robot's left = viewer's right
+
+
+def test_box_blur_conserves_energy():
+    b = np.zeros((H, W), np.float32)
+    b[120, 120] = 1.0
+    out = box_blur(b, 2)
+    assert abs(out.sum() - 1.0) < 1e-3
+    assert np.allclose(out[118:123, 118:123], 1 / 25, atol=1e-5)
+
+
+def test_rgb565_frame_matches_rgb_frame():
+    a = FaceRenderer(state='idle', seed=3)
+    b = FaceRenderer(state='idle', seed=3)
+    rgb, raw = None, None
+    for i in range(1, 40):
+        rgb = a.frame(i / 30, 1 / 30)
+        raw = b.frame(i / 30, 1 / 30, 'rgb565')
+    assert len(raw) == H * W * 2
+    px = np.frombuffer(raw, '>u2').reshape(H, W)
+    assert np.array_equal(px >> 11, rgb[..., 0] >> 3)
+    assert np.array_equal((px >> 5) & 0x3F, rgb[..., 1] >> 2)
+    assert np.array_equal(px & 0x1F, rgb[..., 2] >> 3)
+
+
+@pytest.mark.parametrize('rotation', [90, 180, 270])
+def test_rotation_turns_the_frame_counter_clockwise(rotation):
+    base = FaceRenderer(state='idle', seed=5, rotation=0)
+    turned = FaceRenderer(state='idle', seed=5, rotation=rotation)
+    a = b = None
+    for i in range(1, 30):
+        a = base.frame(i / 30, 1 / 30)
+        b = turned.frame(i / 30, 1 / 30)
+    assert np.array_equal(b, np.rot90(a, rotation // 90))
+
+
+def test_bad_rotation_rejected():
+    with pytest.raises(ValueError):
+        FaceRenderer(rotation=45)