fix(desktop): provision JDK 25 in the offline Flatpak sandbox

The JBR 25 toolchain bump (#6203) raised desktopApp's jvmToolchain to
languageVersion 25, but the offline manifest still provisioned only the
openjdk21 SDK extension. With toolchain auto-provisioning disabled (the
build is offline by design), compileJava failed on both arches with
'Cannot find a Java installation matching languageVersion=25'. Swap to
the openjdk25 extension and note the coupling in the manifest.

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

Author: jamesarich

scripts/verify-flatpak/desktop-offline.yaml

@@ -11,7 +11,10 @@ runtime: org.freedesktop.Platform
 runtime-version: '25.08'
 sdk: org.freedesktop.Sdk
 sdk-extensions:
-  - org.freedesktop.Sdk.Extension.openjdk21
+  # Must match desktopApp's jvmToolchain languageVersion — the offline build disables
+  # toolchain auto-provisioning, so a toolchain bump without updating this extension
+  # (and the three /usr/lib/sdk/openjdk* paths below) fails at compileJava.
+  - org.freedesktop.Sdk.Extension.openjdk25
 command: meshtastic-wrapper.sh
 
 finish-args:
@@ -56,9 +59,9 @@ modules:
   - name: meshtastic-desktop
     buildsystem: simple
     build-options:
-      append-path: "/usr/lib/sdk/openjdk21/bin"
+      append-path: "/usr/lib/sdk/openjdk25/bin"
       env:
-        JAVA_HOME: /usr/lib/sdk/openjdk21/jvm/openjdk-21
+        JAVA_HOME: /usr/lib/sdk/openjdk25/jvm/openjdk-25
         # Point Gradle at the offline mirror produced by flatpak-sources.json
         GRADLE_USER_HOME: /run/build/meshtastic-desktop/.gradle
     build-commands:
@@ -73,7 +76,7 @@ modules:
       - sed -i 's|distributionUrl=.*|distributionUrl=gradle-all.zip|' gradle/wrapper/gradle-wrapper.properties
       - echo "org.gradle.java.installations.auto-detect=false" >> gradle.properties
       - echo "org.gradle.java.installations.auto-download=false" >> gradle.properties
-      - echo "org.gradle.java.installations.paths=/usr/lib/sdk/openjdk21/jvm/openjdk-21" >> gradle.properties
+      - echo "org.gradle.java.installations.paths=/usr/lib/sdk/openjdk25/jvm/openjdk-25" >> gradle.properties
       - >
         sed -i
         's/^\(\s*\)vendor\.set(JvmVendorSpec\.JETBRAINS)/\1\/\/ vendor.set(JvmVendorSpec.JETBRAINS)/'