Show banner when app is built from source

[kmcginnes]

When running the app locally (e.g., vite dev or docker build without version info), users should see a banner indicating they are on a source build.

Proposal

• Detect missing APP_VERSION or mark via env var IS_SOURCE_BUILD=true.
• Show banner in the UI: "Running a local development build".
• Should not appear in CI/CD release images.

Acceptance Criteria

• Banner appears for local/dev builds with no release version.
• Banner is absent in Docker images built by CI/CD pipelines.