ci: migrate image registry from ghcr.io to git.farh.net

Replace GitHub Container Registry with Gitea's built-in container registry.
- REGISTRY env var: ghcr.io -> git.farh.net
- All 4 build-and-push jobs: replace GHCR login with Gitea registry login
  using cs_carl + GITEA_TOKEN (token already required for infra checkout)
- deploy-dev/deploy-uat: update kustomize image refs to git.farh.net/*
- Also fix legacy api/.gitea/workflows/ci.yml (non-executing nested file)

Required secrets drop from 5 to 3: DOCKERHUB_USERNAME, DOCKERHUB_TOKEN,
GITEA_TOKEN. GHCR_USERNAME and GHCR_TOKEN no longer needed.

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

api/.gitea/workflows/ci.yml

@@ -15,7 +15,7 @@ permissions:
   packages: write
 
 env:
-  REGISTRY: ghcr.io
+  REGISTRY: git.farh.net
   IMAGE_NAME: cartsnitch/api
 
 jobs:
@@ -130,13 +130,13 @@ jobs:
           username: ${{ secrets.DOCKERHUB_USERNAME }}
           password: ${{ secrets.DOCKERHUB_TOKEN }}
 
-      - name: Log in to GHCR
+      - name: Log in to Gitea registry
         if: github.event_name == 'push' && github.ref == 'refs/heads/main'
         uses: docker/login-action@v3
         with:
           registry: ${{ env.REGISTRY }}
-          username: ${{ github.actor }}
-          password: ${{ secrets.GITHUB_TOKEN }}
+          username: cs_carl
+          password: ${{ secrets.GITEA_TOKEN }}
 
       - name: Extract metadata
         id: meta