fix: include API/ in backend Docker image

Build context was ./backend so API/ was never copied into the image.
server.js imports ../API/index.js which resolves to /API/index.js at runtime.
Expand build context to project root and explicitly copy API/ to /API/.

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

docker-compose.yml

@@ -5,7 +5,9 @@ services:
 
   backend:
     image: git.hacecalor.net/ichitux/farmafinder-backend:latest
-    build: ./backend
+    build:
+      context: .
+      dockerfile: backend/Dockerfile
     restart: unless-stopped
     ports:
       - "3001:3001"