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>

README.md

@@ -0,0 +1,62 @@
+# matrix-pi
+
+Backup of the Pimoroni LTP-305G LED matrix display setup running on `matrixpi`
+under the `dissimulo` user. Two LTP-305G modules are wired to the I2C bus and
+display the current time as a clock — hour on the left module (I2C `0x61`),
+minute on the right (I2C `0x63`).
+
+## Hardware
+
+- Raspberry Pi (running Debian Bookworm, kernel 6.6.x)
+- 2 × Pimoroni LTP-305G breakouts on I2C bus 1
+  - `0x61` — hour digits
+  - `0x63` — minute digits
+
+## What's in here
+
+| Path | Purpose |
+| --- | --- |
+| `systemd/` | The two systemd units that run the clock at boot |
+| `deployed/` | Mirror of the on-disk script tree the units invoke (includes the local `%I` 12-hour customization to `clock.py`) |
+| `vendor/ltp305-python/` | Vendored copy of the Pimoroni `ltp305` Python library (offline install fallback) |
+| `vendor/breakout-garden/` | Vendored copy of Pimoroni's Breakout Garden tooling (used for I2C autodetect) |
+| `config/boot-firmware-config.txt.snippet` | The `/boot/firmware/config.txt` lines that enable I2C |
+| `install.sh` | Idempotent restore script |
+| `docs/inventory.md` | Source-of-truth inventory of every LTP-305G-related file on the live system |
+
+## Restoring on a fresh Pi
+
+1. Flash Raspberry Pi OS (Bookworm or later), create user `dissimulo`.
+2. Ensure I2C is enabled — either via `raspi-config` or by appending the line
+   from `config/boot-firmware-config.txt.snippet` to `/boot/firmware/config.txt`
+   and rebooting.
+3. Wire the two LTP-305G breakouts; confirm with `i2cdetect -y 1` that they
+   appear at `0x61` and `0x63`. (Install `i2c-tools` if missing.)
+4. From a clone of this repo, run:
+
+   ```
+   sudo ./install.sh
+   ```
+
+   This installs the `ltp305` Python package from `vendor/`, drops the
+   customized scripts into `/home/dissimulo/Pimoroni/ltp305/`, and enables both
+   systemd units.
+
+5. Verify:
+
+   ```
+   systemctl status matrix0x61.service matrix0x63.service
+   ```
+
+## Local customization vs. upstream
+
+The deployed `clock.py` differs from the upstream Pimoroni `ltp305-python`
+example by one line — the `hour` format is `%I` (12-hour) instead of `%H`
+(24-hour). This is preserved in `deployed/home/dissimulo/Pimoroni/ltp305/examples/clock.py`.
+
+## Upstream provenance
+
+Vendored sources were captured from these commits:
+
+- `pimoroni/ltp305-python` @ `bf859fe6cddf8cffcb12d62bad8f21e0bbb9fc42`
+- `pimoroni/breakout-garden` @ `9c331458ee8c4732dbc783a6409ef53d671d321b`