Add Gitea self-hosted git/CI/registry to replace GitHub

Deploy Gitea via Helm with dedicated CloudNativePG database,
in-cluster Actions runner (DinD), and built-in container registry.
ArgoCD repoURLs updated to use in-cluster Gitea SSH. Preview
ApplicationSet switched from GitHub PR generator to Gitea PR
generator. App images now pull from gitea.coreworlds.io registry.

Remaining setup after deploy: seal runner token, ArgoCD API token,
and registry pull secret once Gitea is running. Add ArgoCD deploy
key to Gitea repo settings.

.gitea/workflows/deploy-preview.yaml

@@ -0,0 +1,64 @@
+name: Deploy Preview
+
+on:
+  pull_request:
+    types: [opened, synchronize, reopened]
+
+jobs:
+  deploy:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+
+      - uses: pnpm/action-setup@v4
+
+      - uses: actions/setup-node@v4
+        with:
+          node-version: 20
+          cache: pnpm
+
+      - run: pnpm install --frozen-lockfile
+
+      - name: Determine changed apps
+        id: changes
+        run: |
+          APPS=$(pnpm turbo build --filter='...[origin/main]' --dry-run=json | jq -r '[.packages[] | select(startswith("@homelab/")) | sub("@homelab/";"") ] | join(",")')
+          echo "apps=$APPS" >> "$GITHUB_OUTPUT"
+
+      - name: Build and push images
+        if: steps.changes.outputs.apps != ''
+        run: |
+          echo "${{ secrets.GITEA_TOKEN }}" | docker login gitea.coreworlds.io -u ${{ gitea.actor }} --password-stdin
+          IFS=',' read -ra APPS <<< "${{ steps.changes.outputs.apps }}"
+          for app in "${APPS[@]}"; do
+            docker build \
+              -t gitea.coreworlds.io/julia/homelab-${app}:${{ gitea.sha }} \
+              apps/${app}
+            docker push gitea.coreworlds.io/julia/homelab-${app}:${{ gitea.sha }}
+          done
+
+      - name: Update image tags in preview overlay
+        if: steps.changes.outputs.apps != ''
+        run: |
+          IFS=',' read -ra APPS <<< "${{ steps.changes.outputs.apps }}"
+          for app in "${APPS[@]}"; do
+            cd apps/${app}/k8s/overlays/preview
+            kustomize edit set image gitea.coreworlds.io/julia/homelab-${app}=gitea.coreworlds.io/julia/homelab-${app}:${{ gitea.sha }}
+            cd -
+          done
+
+      - name: Comment preview URL
+        uses: actions/github-script@v7
+        with:
+          script: |
+            const { owner, repo } = context.repo;
+            const issue_number = context.issue.number;
+            const body = `## Preview Deploy\nNamespace: \`preview-${issue_number}\`\nArgoCD will sync automatically from branch \`${context.payload.pull_request.head.ref}\`.`;
+            await fetch(`${process.env.GITHUB_API_URL}/repos/${owner}/${repo}/issues/${issue_number}/comments`, {
+              method: 'POST',
+              headers: {
+                'Authorization': `token ${process.env.GITHUB_TOKEN}`,
+                'Content-Type': 'application/json'
+              },
+              body: JSON.stringify({ body })
+            });