feat: set up signed release pipeline for Forgejo

Adds env-var-driven release signing, fastlane metadata for F-Droid/Obtainium
listings, and a tag-triggered .forgejo workflow that builds, signs, and
publishes the APK as a Forgejo release.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

.forgejo/workflows/release.yml

@@ -0,0 +1,57 @@
+name: Release APK
+
+on:
+  push:
+    tags: ["v*"]
+
+jobs:
+  build:
+    runs-on: android
+
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: Extract version
+        run: |
+          VERSION=$(grep '^version:' pubspec.yaml | sed 's/version: //')
+          echo "VERSION_CODE=$(echo "$VERSION" | grep -oP '(?<=\+)\d+')" >> $GITHUB_ENV
+          echo "VERSION_NAME=$(echo "$VERSION" | grep -oP '^[^+]+')" >> $GITHUB_ENV
+
+      - name: Decode keystore
+        run: |
+          echo "${{ secrets.KEYSTORE_BASE64 }}" | base64 -d > android/app/release.jks
+          echo "KEYSTORE_PATH=$GITHUB_WORKSPACE/android/app/release.jks" >> $GITHUB_ENV
+
+      - name: Build release APK
+        env:
+          STORE_PASSWORD: ${{ secrets.STORE_PASSWORD }}
+          KEY_ALIAS:      ${{ secrets.KEY_ALIAS }}
+          KEY_PASSWORD:   ${{ secrets.KEY_PASSWORD }}
+        run: |
+          env -u GITHUB_TOKEN -u GH_TOKEN -u JAVA_HOME \
+            devbox run -- flutter build apk --release
+
+      - name: Create release and upload APK
+        env:
+          FORGEJO_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+        run: |
+          APK="muzzlevelocity-${{ env.VERSION_NAME }}.apk"
+          cp build/app/outputs/flutter-apk/app-release.apk "$APK"
+
+          BODY=$(python3 -c "
+          import json
+          print(json.dumps(open('fastlane/metadata/android/en-US/changelogs/${{ env.VERSION_CODE }}.txt').read().strip()))
+          ")
+
+          RELEASE_ID=$(curl -sf -X POST \
+            -H "Authorization: token $FORGEJO_TOKEN" \
+            -H "Content-Type: application/json" \
+            "$GITHUB_SERVER_URL/api/v1/repos/$GITHUB_REPOSITORY/releases" \
+            -d "{\"tag_name\":\"$GITHUB_REF_NAME\",\"name\":\"$GITHUB_REF_NAME\",\"body\":$BODY}" \
+            | python3 -c 'import sys,json; print(json.load(sys.stdin)["id"])')
+
+          curl -sf -X POST \
+            -H "Authorization: token $FORGEJO_TOKEN" \
+            -H "Content-Type: application/vnd.android.package-archive" \
+            "$GITHUB_SERVER_URL/api/v1/repos/$GITHUB_REPOSITORY/releases/$RELEASE_ID/assets?name=$APK" \
+            --data-binary @"$APK"