feat: dynamic app version sourced from root VERSION file

Replaces the hardcoded version string in SettingsPage.tsx with a single
source of truth: a /VERSION file at the repo root. To cut a new release,
edit only that one file.

Frontend:
- vite.config.ts reads /VERSION at dev-server startup and injects it as
  the __APP_VERSION__ global via Vite's define mechanism (compile-time,
  zero runtime cost). Falls back to VITE_APP_VERSION env var for prod
  Docker builds that pass it as a build arg.
- vite-env.d.ts adds the TypeScript declaration for __APP_VERSION__.
- SettingsPage.tsx Badge now renders {__APP_VERSION__} instead of the
  literal string.

Backend:
- app.controller.ts reads /VERSION once at module load and includes
  "version" in both GET /api and GET /api/health responses.
- NewRelicTransactionInterceptor tags every NR transaction with
  newrelic.addCustomAttribute('appVersion', version) so releases can be
  compared in NRQL: SELECT average(duration) FROM Transaction WHERE
  appVersion = '2026.5.22'

Docker:
- docker-compose.yml mounts ./VERSION:/app/VERSION:ro in both backend
  and frontend dev containers.
- Production Dockerfiles include COPY VERSION ./ with a comment
  instructing CI to copy the root VERSION into each build context before
  docker build.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

docker-compose.yml

@@ -60,6 +60,7 @@ services:
       - ./backend/nest-cli.json:/app/nest-cli.json
       - ./backend/tsconfig.json:/app/tsconfig.json
       - ./backend/tsconfig.build.json:/app/tsconfig.build.json
+      - ./VERSION:/app/VERSION:ro
     depends_on:
       postgres:
         condition: service_healthy
@@ -80,6 +81,7 @@ services:
       - ./frontend/src:/app/src
       - ./frontend/index.html:/app/index.html
       - ./frontend/vite.config.ts:/app/vite.config.ts
+      - ./VERSION:/app/VERSION:ro
     depends_on:
       - backend
     networks: