Add Nomad deployment configuration and CI/CD pipeline

- Add docker.nix for Nix-based Docker image builds
- Update flake.nix with dockerImage package output
- Add output: standalone to next.config.ts for production builds
- Add /metrics endpoint for Prometheus scraping
- Add Gitea Actions workflow calling shared deploy-nomad.yaml

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

.gitea/workflows/deploy.yaml

@@ -0,0 +1,16 @@
+# ABOUTME: Gitea Actions workflow for deploying PhaseFlow to Nomad.
+# ABOUTME: Builds Nix Docker image and deploys using shared workflow.
+
+name: Deploy
+
+on:
+  push:
+    branches: [main]
+  workflow_dispatch:
+
+jobs:
+  deploy:
+    uses: alo/alo-cluster/.gitea/workflows/deploy-nomad.yaml@master
+    with:
+      service_name: phaseflow
+    secrets: inherit