chore(#353): add drift codegen to the release pipeline's build jobs

Follow-up to #348 (now merged): dev has drift, but release-signed.yml
had no build_runner step, so the next v* release would fail its
android/windows/linux builds on the missing offband_database.g.dart.

Adds `dart run build_runner build --delete-conflicting-outputs` after
`flutter pub get` in the three jobs that build (android, windows,
linux). gate and release don't compile Dart, so no codegen there.

Matches the step #348 added to build.yml/flutter_dart/deploy-web. This
one couldn't ride #348 because release-signed.yml had diverged on dev
(#342/#346) and editing the stale copy caused a merge conflict — see
#348 discussion.

Part of epic #312. Agent: SapphireCompass (session 8d755b5e)

.github/workflows/release-signed.yml

@@ -98,6 +98,7 @@ jobs:
           echo "Keystore decoded (${SIZE} bytes), key.properties written."
 
       - run: flutter pub get
+      - run: dart run build_runner build --delete-conflicting-outputs
       - name: Write dart_defines.json
         env:
           GIPHY_API_KEY: ${{ secrets.GIPHY_API_KEY }}
@@ -182,6 +183,7 @@ jobs:
           flutter-version: "3.44.1"
           cache: true
       - run: flutter pub get
+      - run: dart run build_runner build --delete-conflicting-outputs
       - name: Write dart_defines.json
         env:
           GIPHY_API_KEY: ${{ secrets.GIPHY_API_KEY }}
@@ -210,6 +212,7 @@ jobs:
       - name: Install Linux build deps
         run: sudo apt-get update && sudo apt-get install -y clang cmake ninja-build pkg-config libgtk-3-dev
       - run: flutter pub get
+      - run: dart run build_runner build --delete-conflicting-outputs
       - name: Write dart_defines.json
         env:
           GIPHY_API_KEY: ${{ secrets.GIPHY_API_KEY }}