ci: lower Angular build peak memory on Pi

Serialize esbuild/Angular workers and cap the Node heap under the
2GiB Drone step limit so SSR builds trade time for surviving OOM.

Co-authored-by: Cursor <cursoragent@cursor.com>

.drone.yml

@@ -15,6 +15,9 @@ steps:
   - name: build
     image: oven/bun:1-alpine
     environment:
+      # Serialise Angular workers — lower peak RAM, longer build (Pi-friendly)
+      NG_BUILD_MAX_WORKERS: "1"
+      NODE_OPTIONS: "--max-old-space-size=1536"
       STRAVA_CLIENT_ID:
         from_secret: strava_client_id
       STRAVA_REDIRECT_URI: