docs: add related-projects section to README

Links to c-base/dmxbackend (the backend this tool talks to), the
matelight ecosystem (jaseg/matelight upstream, c-base fork,
matelight-pixel frontend, the c-matelight gitea org with the freshest
code, and mlaudiospectrum for the audio-reactive prior art), other
c-base lighting (roboclub-lighting), and the artefact guide entry for
the Matelight hardware history.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

README.md

@@ -268,3 +268,53 @@ Source layout:
 - **Photosensitivity.** Gabba/Red/Blue/Pink strobes are hard 12.5 Hz
   square-wave alternations at the engine's Nyquist rate. Don't fire
   them at a crowd that hasn't been warned.
+
+---
+
+## Related projects
+
+### c-base backend & infrastructure
+
+- **[c-base/dmxbackend](https://github.com/c-base/dmxbackend)** — the
+  aiohttp service this tool talks to. ArtNet/HTTP-WebSocket/MQTT bridge
+  for the mainhall lights. Hosts the fixture API at
+  `dmx.cbrp3.c-base.org:8000` and the live state WebSocket at
+  `/api/v1/websocket_state/`.
+- **[c-base/c-base-map](https://github.com/c-base/c-base-map)** —
+  interactive map of c-base areas and interfaces. Useful context for
+  where the fixtures actually sit in space.
+- **[code.c-base.org/t/dmx-mainhall-foo](https://code.c-base.org/t/dmx-mainhall-foo)** —
+  this repo's home.
+
+### Matelight ecosystem
+
+- **[jaseg/matelight](https://github.com/jaseg/matelight)** — the
+  canonical project. WS2801-in-Mate-bottles, 40×16 display, CRAP
+  protocol (UDP/1337). Foundation everything else builds on.
+- **[c-base/matelight](https://github.com/c-base/matelight)** — c-base
+  fork of the above.
+- **[c-base/matelight-pixel](https://github.com/c-base/matelight-pixel)**
+  — Python/FastAPI + React frontend served at
+  `matelight.cbrp3.c-base.org:8000`.
+- **[code.c-base.org/c-matelight](https://code.c-base.org/c-matelight)**
+  — the active production org on c-base's Gitea (fresher than the
+  GitHub mirror). Contains `matelight`, `matelight-original`,
+  `matelight-pixel`, `c-matelight`.
+- **[c-base/mlaudiospectrum](https://github.com/c-base/mlaudiospectrum)**
+  — audio-spectrum analyzer that paints the Matelight from mic input.
+  Conceptually adjacent to our `BeatPulse` preset; if you want to push
+  audio reactivity into the Matelight itself (instead of the hall),
+  this is the prior art.
+
+### Other c-base lighting
+
+- **[c-base/roboclub-lighting](https://github.com/c-base/roboclub-lighting)**
+  — separate lighting project for the roboclub area, C/MCU-side.
+
+### Documentation
+
+- **[cbag3.c-base.org/artefact/matelight](https://cbag3.c-base.org/artefact/matelight)**
+  — c-base artefact guide entry for the Matelight (hardware history,
+  build notes).
+- **[c-base/artefact-guide](https://github.com/c-base/artefact-guide)**
+  — source of the artefact guide above.