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

pi/display_test.py

@@ -0,0 +1,64 @@
+#!/usr/bin/env python3
+"""Draw a test pattern on the BrainCraft HAT's ST7789 (240x240, SPI CE0, DC=GPIO25, BL=GPIO26).
+
+  display_test.py [ROTATION]     one pattern, then a frame-rate probe
+
+The driver rotates in software (PIL, counter-clockwise), and the panel's 80-row RAM offset belongs
+to the glass, so y_offset=80 holds for every rotation. 270 is the mounted pose (microSD end up).
+A correct picture has the frame complete on all four edges, no noise, the white triangle in the
+top-left corner as you look at the panel in its mounted pose, and upright text.
+"""
+import sys
+import time
+
+import board
+import digitalio
+from adafruit_rgb_display import st7789
+from PIL import Image, ImageDraw, ImageFont
+
+W = H = 240
+
+
+def make_display(rotation, x_offset, y_offset, baudrate=48_000_000):
+    return st7789.ST7789(
+        board.SPI(),
+        cs=None,  # CE0 is driven by the kernel SPI driver; claiming GPIO8 fails with 'GPIO busy'
+        dc=digitalio.DigitalInOut(board.D25),
+        rst=None,
+        baudrate=baudrate,
+        width=W,
+        height=H,
+        x_offset=x_offset,
+        y_offset=y_offset,
+        rotation=rotation,
+    )
+
+
+def pattern(label):
+    img = Image.new("RGB", (W, H), "black")
+    d = ImageDraw.Draw(img)
+    for i, c in enumerate(["red", "lime", "blue", "yellow", "cyan", "magenta"]):
+        d.rectangle([i * 40, 90, i * 40 + 39, 150], fill=c)
+    d.rectangle([0, 0, W - 1, H - 1], outline="white")      # edge frame: shows offset/clipping
+    d.rectangle([3, 3, W - 4, H - 4], outline="gray")
+    d.polygon([(8, 8), (58, 8), (8, 58)], fill="white")      # top-left marker: shows rotation
+    d.text((70, 12), label[0], fill="white", font=ImageFont.load_default(size=48))
+    d.text((70, 66), label[1], fill="white", font=ImageFont.load_default(size=14))
+    for x in range(0, W, 30):
+        d.line([(x, 160), (x, H - 8)], fill="gray")
+    for y in range(160, H - 8, 20):
+        d.line([(0, y), (W, y)], fill="gray")
+    return img
+
+
+backlight = digitalio.DigitalInOut(board.D26)
+backlight.switch_to_output(value=True)
+
+rotation = int(sys.argv[1]) if len(sys.argv) > 1 else 270
+disp = make_display(rotation, 0, 80)
+img = pattern((str(rotation), f"rot={rotation} y_off=80"))
+disp.image(img)
+t0, n = time.monotonic(), 30
+for _ in range(n):
+    disp.image(img)
+print(f"pattern shown; full-frame push rate {n / (time.monotonic() - t0):.1f} fps at 48 MHz")