Add seed Docker stage and push migrate/seed images in CI (#37)

- Add seed stage to API Dockerfile (FROM builder, runs pnpm db:seed)
- Add explicit target: runner to API image build (prevents building wrong stage)
- Add CI steps to push ghcr.io/groombook/migrate and ghcr.io/groombook/seed images

Co-authored-by: Groom Book CEO <ceo@groombook.dev>
Co-authored-by: Paperclip <noreply@paperclip.ing>

.github/workflows/ci.yml

@@ -94,6 +94,7 @@ jobs:
         with:
           context: .
           file: apps/api/Dockerfile
+          target: runner
           push: true
           tags: |
             ghcr.io/groombook/api:${{ github.sha }}
@@ -101,6 +102,32 @@ jobs:
           cache-from: type=gha
           cache-to: type=gha,mode=max
 
+      - name: Build and push Migrate image
+        uses: docker/build-push-action@v6
+        with:
+          context: .
+          file: apps/api/Dockerfile
+          target: migrate
+          push: true
+          tags: |
+            ghcr.io/groombook/migrate:${{ github.sha }}
+            ghcr.io/groombook/migrate:latest
+          cache-from: type=gha
+          cache-to: type=gha,mode=max
+
+      - name: Build and push Seed image
+        uses: docker/build-push-action@v6
+        with:
+          context: .
+          file: apps/api/Dockerfile
+          target: seed
+          push: true
+          tags: |
+            ghcr.io/groombook/seed:${{ github.sha }}
+            ghcr.io/groombook/seed:latest
+          cache-from: type=gha
+          cache-to: type=gha,mode=max
+
       - name: Build and push Web image
         uses: docker/build-push-action@v6
         with: