ci: cap Gradle below 9.6, which no AGP 8.x can build with

Dependabot proposed Gradle 9.7.1 (#13) and it broke the Android build:

    Plugin 'com.android.internal.application' relies on
    'org.gradle.api.problems.internal.InternalProblems', a Gradle internal
    API that was removed in Gradle 9.6.0. ... or use Gradle 9.5.

Gradle 9.6.0 dropped an internal API that every AGP 8.x depends on. AGP is
deliberately held at 8.x here because AGP 9 is not Flutter-ready, so the two
are coupled: Gradle cannot move past 9.5 until that migration happens.

The previous rule only ignored Gradle *majors*, so 9.6+ sailed through as a
minor. Nothing would have stopped it: ci.yml runs format, analyze and test,
none of which invoke Gradle, so #13's `validate` check passed green while the
app could not build at all. Caught by building locally rather than trusting
the check.

Verified by isolation — Gradle 9.7.1 + AGP 8.13.2 fails; Gradle 9.3.1 with
the same AGP 8.13.2 and protobuf 4.36.1 builds. Lift this cap together with
the AGP 9 move.

Author: i99dev

.github/dependabot.yml

@@ -18,13 +18,28 @@ updates:
     open-pull-requests-limit: 3
     labels: ["dependencies"]
     # The Flutter ecosystem (3.47.2 + common plugins like audio_session)
-    # isn't ready for AGP 9, Kotlin 2.3, or Gradle 9. Holding these until
-    # Flutter and plugins migrate to built-in Kotlin + the new DSL.
+    # isn't ready for AGP 9 or Kotlin 2.3. Holding these until Flutter and
+    # plugins migrate to built-in Kotlin + the new DSL.
     # AGP 9.x specifically introduces breaking changes (built-in Kotlin,
     # new DSL, kotlinOptions removal) that Flutter's gradle plugin does
     # not yet support — verified on Flutter 3.47.2. Patch + minor under
     # the current majors still come through.
     # Track https://docs.flutter.dev/release/breaking-changes/migrate-to-built-in-kotlin
+    #
+    # Gradle is capped at 9.5.x, which is tighter than "no majors". Gradle
+    # 9.6.0 removed the internal `org.gradle.api.problems.internal.
+    # InternalProblems` API that every AGP 8.x relies on, so 9.6+ fails the
+    # build outright:
+    #
+    #   Plugin 'com.android.internal.application' relies on
+    #   'org.gradle.api.problems.internal.InternalProblems', a Gradle internal
+    #   API that was removed in Gradle 9.6.0. ... or use Gradle 9.5.
+    #
+    # Because AGP is pinned to 8.x above, the two are coupled: Gradle cannot
+    # move past 9.5 until AGP 9 becomes viable. Nothing in CI catches this —
+    # ci.yml never runs Gradle — so a 9.6+ bump looks green and breaks every
+    # release build. Verified locally: Gradle 9.7.1 + AGP 8.13.2 fails,
+    # 9.3.1 + AGP 8.13.2 builds. Lift this together with the AGP 9 move.
     ignore:
       - dependency-name: "com.android.application"
         update-types: ["version-update:semver-major"]
@@ -35,7 +50,7 @@ updates:
       - dependency-name: "org.jetbrains.kotlin:kotlin-gradle-plugin"
         update-types: ["version-update:semver-major", "version-update:semver-minor"]
       - dependency-name: "gradle"
-        update-types: ["version-update:semver-major"]
+        versions: [">=9.6"]
 
   - package-ecosystem: "github-actions"
     directory: "/"