feat: add skills, version pinning, CI/CD, and generated-file headers

- Create skills: rego-pd-validator, usb-gadget-configfs, led-matrix-msgpack-rpc
- Update pd-audio-synthesis skill with Uno Q specifics
- Add Pd version check (min 0.54.0) to start-synth.sh
- Add DO NOT EDIT headers to generated pd patches
- Add Gitea Actions CI workflow for patch validation
- Add ConditionPathExists guards to legacy systemd services
- Add 'just ci' recipe for CI

scripts/gen_mpk_sim.py

@@ -93,7 +93,10 @@ def gen():
         connect(c, msg, 0, ns, 0)
 
     # ── Write (Pd format: #X obj for objects, #X msg/text/floatatom/symbol for others) ──
-    lines = ["#N canvas 0 0 950 490 10;"]
+    lines = [
+        "#N canvas 0 0 950 490 10;",
+        "# DO NOT EDIT — generated by scripts/gen_mpk_sim.py;",
+    ]
     obj_types = {"bng","t","del","netsend","loadbang","hsl","comment"}
     for x, y, *args in o:
         etype = args[0]