ci: remove GitHub CI — native git.hanzo.ai + cd.hanzo.ai only

This workflow ran on a self-hosted actions-runner-controller pool. ARC is
being decommissioned: CI executes inside git.hanzo.ai (Gitea Actions,
.hanzo/workflows) and delivery is cd.hanzo.ai reconciling the reviewed image
pin in hanzoai/universe. GitHub is a mirror and runs nothing.

Removed rather than repointed — there is no GitHub-side pool to move to, and
leaving it would keep ARC load-bearing.

.github/workflows/deploy-site.yml

@@ -1,50 +0,0 @@
-name: Build papers.hanzo.ai image
-
-# Build the static papers-site image on Hanzo's own infrastructure: the
-# self-hosted arcd pool (no GitHub-hosted builders, no Pages artifact quota),
-# pushed to GHCR. DEPLOY is handled natively by platform.hanzo.ai (operator
-# rollout onto the `papers` Service CR) — CI never touches DOKS directly.
-# The build→deploy handoff is wired via the Hanzo Platform GitHub App +
-# .platform.yml (see PLATFORM_CI). Until that webhook is live this workflow
-# just publishes the image; the platform performs the rollout.
-
-on:
-  push:
-    branches: [main]
-    paths:
-      - 'site/**'
-      - '.github/workflows/deploy-site.yml'
-  workflow_dispatch:
-
-concurrency:
-  group: papers-build
-  cancel-in-progress: true
-
-env:
-  IMAGE: ghcr.io/hanzoai/papers
-
-jobs:
-  build:
-    runs-on: hanzo-build-linux-amd64        # self-hosted arcd (hanzoai org)
-    permissions:
-      contents: read
-      packages: write
-    steps:
-      - uses: actions/checkout@v4
-      - uses: docker/setup-buildx-action@v3
-      - name: Log in to GHCR
-        uses: docker/login-action@v3
-        with:
-          registry: ghcr.io
-          username: ${{ github.actor }}
-          password: ${{ secrets.GITHUB_TOKEN }}
-      - name: Build and push static-site image
-        uses: docker/build-push-action@v6
-        with:
-          context: ./site
-          file: ./site/Dockerfile
-          push: true
-          provenance: false
-          tags: |
-            ${{ env.IMAGE }}:${{ github.sha }}
-            ${{ env.IMAGE }}:main