Initial backup of LTP-305G matrix clock setup on matrixpi

Captures everything needed to redeploy the two-display clock (hour on I2C
0x61, minute on I2C 0x63) on a fresh Pi:

- Both systemd units (matrix0x61.service, matrix0x63.service)
- Deployed Pimoroni script tree, including the local %I (12-hour) clock
  customization
- Vendored upstream sources (ltp305-python, breakout-garden) so restore is
  fully offline-capable
- Boot config snippet enabling I2C
- install.sh that wires it all back up idempotently
- Inventory doc cross-referencing every live-system path

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

vendor/breakout-garden/examples/rainbow-compass/rainbow-compass.py

@@ -0,0 +1,100 @@
+#!/usr/bin/env python3
+
+import time
+import math
+import colorsys
+from lsm303d import LSM303D
+from rgbmatrix5x5 import RGBMatrix5x5
+
+print("""This Pimoroni Breakout Garden example requires an LSM303D
+Motion Sensor Breakout and a 5x5 RGB Matrix Breakout.
+
+The Rainbow Compass calculates and displays compass heading as an
+RGB colour around the hue wheel, with North being red, South cyan,
+East green, and West purple, appromximately.
+
+Press Cyrl-+C to exit.
+""")
+
+
+def raw_heading(minimums, maximums, zero=0):
+    """Return a raw compass heading calculated from the magnetometer data."""
+
+    X = 0
+    Y = 2  # Change to 1 if you have the breakout flat
+
+    # The range over which values will be calculated, i.e. -1 to +1
+    mag_range = 2
+
+    # Get the magnetometer's values
+    mag = list(lsm.magnetometer())
+
+    # Scale and shift values
+    for i in range(len(mag)):
+        mag[i] = ((mag_range / (maximums[i] - minimums[i])) * mag[i]) - \
+                 (mag_range / 2.0)
+
+    # Calculate the heading from the vector
+    heading = math.atan2(mag[Y], mag[X])
+
+    if heading < 0:
+        heading += (2 * math.pi)
+
+    # Convert radian value to degrees
+    heading_degrees = (round(math.degrees(heading), 2) - zero) % 360
+
+    return heading_degrees
+
+
+lsm = LSM303D(0x1d)  # Change to 0x1e if you have soldered the address jumper
+
+# Set up the 5x5 RGB matrix
+rgbmatrix5x5 = RGBMatrix5x5()
+rgbmatrix5x5.set_clear_on_exit()
+rgbmatrix5x5.set_brightness(0.8)
+
+# Python 2/3 compatibility
+try:
+    input = raw_input
+except NameError:
+    pass
+
+input("Lay your LSM303D in Breakout Garden flat (LSM303D vertical), \n\
+press a key to start, then rotate it 360 degrees, keeping it flat...\n")
+
+# Variables to govern calibration time
+t_start = time.time()
+t_elapsed = 0
+calibration_time = 30
+
+# Initial values for mins and maxs
+minimums = list(lsm.magnetometer())
+maximums = list(lsm.magnetometer())
+
+# Run calibration until time limit is reached
+while t_elapsed < calibration_time:
+    mag = lsm.magnetometer()
+    for i in range(len(mag)):
+        if mag[i] < minimums[i]:  # Set new min
+            minimums[i] = mag[i]
+        if mag[i] > maximums[i]:  # Set new max
+            maximums[i] = mag[i]
+    t_elapsed = time.time() - t_start
+
+input("Calibration complete!\n\nIf you want to set a zero (North) point, \n\
+then turn your breakout to that point and press a key...\n")
+
+# Zero point for the compass
+zero = raw_heading(minimums, maximums)
+
+input("Press a key to begin readings!\n")
+
+# Begin compass readings and display on RGB matrix
+while True:
+    rh = raw_heading(minimums, maximums, zero=zero)
+    hue = rh / 360.0  # Hue is based on compass heading
+    r, g, b = [int(c * 255) for c in colorsys.hsv_to_rgb(hue, 1.0, 1.0)]
+    rgbmatrix5x5.set_all(r, g, b)  # Set whole matrix to calculated RGB
+    rgbmatrix5x5.show()
+    print("compass heading: {:0.0f} degrees".format(rh))
+    time.sleep(0.1)