feat(version): /api/version + build-time version/commit stamping

Add a VERSION file (0.1.0) and inject APP_VERSION/GIT_SHA/BUILD_DATE as Docker
build-args (both stages; Vite inlines them into the SPA). New public GET
/api/version returns app_version, git_sha, build_date and the Alembic head as the
database revision. deploy.sh and the localdev build pass the args.

docker-compose.yml

@@ -18,6 +18,10 @@ services:
     build:
       context: .
       dockerfile: Dockerfile
+      args:
+        APP_VERSION: ${APP_VERSION:-dev}
+        GIT_SHA: ${GIT_SHA:-unknown}
+        BUILD_DATE: ${BUILD_DATE:-}
     env_file: .env
     environment:
       DATABASE_URL: postgresql+psycopg://${POSTGRES_USER:-subfeed}:${POSTGRES_PASSWORD:-subfeed}@db:5432/${POSTGRES_DB:-subfeed}