revert: undo PR #47 Dockerfile apps/api switch (broke CI Docker build)

Reverts the Dockerfile to the root src/ build. PR #47 switched to apps/api/
but the pnpm workspace config and lockfile don't include apps/*, causing
Docker build failures (CI runs #968, #970).

The actual admin 500 root cause needs further investigation — it's in the
code/schema changes, not the Dockerfile build path.

Co-Authored-By: Paperclip <noreply@paperclip.ing>

Dockerfile

@@ -42,12 +42,12 @@ CMD ["node", "dist/index.js"]
 
 # Migrate stage — runs drizzle-kit migrate against the database
 FROM builder AS migrate
-CMD ["pnpm", "db:migrate"]
+CMD ["pnpm", "--filter", "@groombook/db", "migrate"]
 
 # Seed stage — populates the database with test data
 FROM builder AS seed
-CMD ["pnpm", "db:seed"]
+CMD ["pnpm", "--filter", "@groombook/db", "seed"]
 
 # Reset stage — drops all tables, re-runs migrations, and re-seeds
 FROM builder AS reset
-CMD ["pnpm", "db:reset"]
+CMD ["pnpm", "--filter", "@groombook/db", "reset"]