Android dev client for agent QA, version 1.4.0

[byteful]

Adds a CI build of the Android debug dev client (arm64) so the agents' new Android QA can run the app on a real Android device on their box, and moves web and mobile to version 1.4.0. No app code changes.

Before you start

• Adds one workflow ("Android dev client") and one dev dependency for the mobile app. It runs on pull requests and main pushes that touch the mobile app or the dependencies, and on demand.
• It is not a required check and needs no secrets. Its only output is a debug APK kept as a run artifact.
• The 1.4.0 bump is here so the TestFlight build this merge starts gets past the store version gate (1.3.1 is the live App Store version). Backend and admin bump in their own "Bump version to v1.4.0" PRs.

Verify

1. Open this PR's Checks tab.
   Expect: a check named "Android dev client (arm64)" that passes.

2. Open that run's summary page and scroll to Artifacts.
   Expect: one artifact named "android-dev-client-" followed by a long hash.

3. Re-run that job from the run page ("Re-run jobs").
   Expect: it passes in a couple of minutes and adds no second artifact. The "Build the debug dev client" step is skipped, because that fingerprint already has a build.

4. After merging, open Actions, then the "Deploy mobile (TestFlight)" run for the merge commit.
   Expect: it passes. TestFlight then shows a 1.4.0 build of civfix.

Regression

1. On this PR's Checks tab, look at the existing checks: "packages (shared + ui)", "community-web" and "community-mobile".
   Expect: all pass as before.
2. After merging, open Actions and look at the runs for the merge commit.
   Expect: "Deploy mobile (Android)" and "Deploy mobile (TestFlight)" run and pass as on any mobile change. The new workflow runs alongside them and doesn't affect them.

Not covered

• Installing and opening the APK on a device: that happens on the agent box, not on GitHub.