Move nightly note-gen, marker, and alerts to the orchestrator

The release notes, commit marker, and Slack alerts are nightly-specific, so
move them out of the build workflows and into nightly-build.yml:

- prepare job reads the previous nightly-build-commit artifact and generates
  the shared changelog once
- iOS/Android builds run in parallel, consuming the notes (iOS via a new
  releaseNotes input); both expose version/build outputs via workflow_call
- per-platform Slack jobs post the notes with that platform's version
- record job advances the marker only after both builds succeed, so a failed
  night's commits roll into the next successful nightly's notes

Also harden the TestFlight key cleanup with a trap ... EXIT so the App Store
Connect private key is removed even if fastlane exits non-zero under bash -e.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

.github/workflows/build-submit-android.yml

@@ -16,6 +16,13 @@ on:
         type: string
         description: Build profile to use
         required: true
+    outputs:
+      package-version:
+        description: Version from package.json
+        value: ${{ jobs.build.outputs.package-version }}
+      version-code:
+        description: Android version code
+        value: ${{ jobs.build.outputs.version-code }}
 
 # Deploys happen via EAS using EXPO_TOKEN; the GITHUB_TOKEN only checks out code
 permissions:
@@ -31,6 +38,7 @@ jobs:
       cancel-in-progress: false
     outputs:
       package-version: ${{ steps.get-build-info.outputs.PACKAGE_VERSION }}
+      version-code: ${{ steps.get-build-info.outputs.BSKY_ANDROID_VERSION_CODE }}
       apk-artifact-name: build-${{ steps.timestamp.outputs.time }}.apk
     steps:
       - name: Check for EXPO_TOKEN