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

.gitea/workflows/validate.yaml

@@ -0,0 +1,21 @@
+name: Validate and Test
+on:
+  push:
+    branches: [main]
+  pull_request:
+    branches: [main]
+
+jobs:
+  validate-patches:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+      - uses: actions/setup-python@v5
+        with:
+          python-version: "3.12"
+      - name: Install dependencies
+        run: |
+          pip install conftest
+      - name: Validate all .pd patches
+        run: |
+          python3 pd-validator/validate.py pd/*.pd