feat: add HDR Notify service addon for Kodi

Kodi service addon that detects HDR/SDR state of the currently playing
video and notifies external services:

- HyperHDR: toggles tone mapping via videomodehdr JSON-RPC command
- Home Assistant: sends HDR state via webhook trigger

Supports Kodi 20 (Nexus) and later. Both targets are independently
configurable with host, port, SSL, and authentication settings.

Includes GitHub Actions workflow to build installable ZIP packages
on every push and publish them as release assets on tags.

.github/workflows/build.yml

@@ -0,0 +1,40 @@
+name: Build Kodi Addon
+
+on:
+  push:
+    branches: [master]
+    tags: ["v*"]
+  pull_request:
+    branches: [master]
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v6
+
+      - name: Extract version from addon.xml
+        id: version
+        run: |
+          version=$(grep -oP 'version="\K[^"]+' service.video.hdrnotify/addon.xml | head -1)
+          echo "version=$version" >> "$GITHUB_OUTPUT"
+          echo "Addon version: $version"
+
+      - name: Build ZIP package
+        run: |
+          zip -r "service.video.hdrnotify-${{ steps.version.outputs.version }}.zip" \
+            service.video.hdrnotify/ \
+            -x "service.video.hdrnotify/.*"
+
+      - name: Upload artifact
+        uses: actions/upload-artifact@v7
+        with:
+          name: service.video.hdrnotify-${{ steps.version.outputs.version }}
+          path: service.video.hdrnotify-${{ steps.version.outputs.version }}.zip
+
+      - name: Create GitHub Release
+        if: startsWith(github.ref, 'refs/tags/v')
+        uses: softprops/action-gh-release@v2
+        with:
+          files: service.video.hdrnotify-${{ steps.version.outputs.version }}.zip
+          generate_release_notes: true