Use the git commit hash as the app version

- Spec header, status pill and footer now document '<env> @ <hash>'
  instead of invented release numbers
- Backend settings expose GIT_COMMIT_HASH / APP_ENV / APP_VERSION,
  mirroring the original app
- Frontend bakes the short hash in at build time and shows it in the
  top bar

frontend/src/lib/version.ts

@@ -0,0 +1,5 @@
+declare const __GIT_COMMIT_HASH__: string;
+
+export const GIT_COMMIT_HASH = __GIT_COMMIT_HASH__;
+export const APP_ENV = import.meta.env.DEV ? "dev" : "prod";
+export const APP_VERSION = `${APP_ENV} @ ${GIT_COMMIT_HASH}`;