M2-M8: renderer, playback backends, GUI/network, commands, multi-version build

- M2: VideoAnchorRenderer draws width\u00d7height quad oriented by facing
- M3: VideoBackend interface + JavaCV (reflection) and WaterMedia (probe) backends
- M4: VideoConfigScreen GUI + 4 typed payloads + NBT persistence via ReadView/WriteView
- M5: stick item useOnBlock place/edit, AttackBlockCallback delete, /videoPlace /videoDelete /videoMute
- M6: per-tick distance attenuation gain = volume * clamp(1 - d/16, 0, 1), mute zeroes gain
- M7: WatermediaProbe (reflection-only; reports unavailable until v2 supports 1.21.6+)
- M8: multi-version build script (1.21.6/1.21.7/1.21.8) + Gitea Actions matrix workflow

.gitea/workflows/build.yml

@@ -0,0 +1,41 @@
+name: build-matrix
+
+on:
+  push:
+    branches: [main]
+    tags: ["v*"]
+  pull_request:
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    strategy:
+      fail-fast: false
+      matrix:
+        include:
+          - mc: "1.21.6"
+            yarn: "1.21.6+build.1"
+            fabric: "0.120.1+1.21.6"
+          - mc: "1.21.7"
+            yarn: "1.21.7+build.8"
+            fabric: "0.129.0+1.21.7"
+          - mc: "1.21.8"
+            yarn: "1.21.8+build.1"
+            fabric: "0.136.1+1.21.8"
+    steps:
+      - uses: actions/checkout@v4
+      - uses: actions/setup-java@v4
+        with:
+          distribution: temurin
+          java-version: 21
+      - name: Build (MC ${{ matrix.mc }})
+        run: |
+          ./gradlew --no-daemon \
+            -Pminecraft_version=${{ matrix.mc }} \
+            -Pyarn_mappings=${{ matrix.yarn }} \
+            -Pfabric_version=${{ matrix.fabric }} \
+            build
+      - uses: actions/upload-artifact@v4
+        with:
+          name: video_player-mc${{ matrix.mc }}
+          path: build/libs/*.jar