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

Inherited upstream workflow, repointed at a self-hosted ARC pool at fork time.
ARC is being decommissioned: CI runs 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.

This repo has no .hanzo/workflows today; it is a fork whose upstream CI we do
not rely on. If it needs a build, it gets a native pipeline — not an ARC pool.

.github/workflows/check_doc.yaml

@@ -1,63 +0,0 @@
-name: Check Documentation
-
-on:
-  pull_request:
-    branches:
-      - '*'
-    paths:
-      - '.github/workflows/check_doc.yaml'
-      - 'docs/**'
-
-jobs:
-
-  docs:
-    name: lint, build and verify
-    runs-on: hanzo-build-linux-amd64
-
-    steps:
-      - name: Check out code
-        uses: actions/checkout@8e8c483db84b4bee98b60c0593521ed34d9990e8 # v6.0.1
-        with:
-          fetch-depth: 0
-
-      - name: Install markdownlint
-        run: |
-          npm install --global [email protected] [email protected]
-
-      - name: Lint
-        run: ./docs/scripts/lint.sh docs
-
-      - name: Setup python
-        uses: actions/setup-python@a309ff8b426b58ec0e2a45f0f869d46889d02405 # v6.2.0
-        with:
-          python-version: '3.12'
-          cache: 'pip'
-          cache-dependency-path: "./docs/requirements.txt"
-
-      - name: Build documentation
-        working-directory: ./docs
-        run: |
-          pip install -r requirements.txt
-          mkdocs build --strict
-
-      - name: Setup ruby
-        uses: ruby/setup-ruby@90be1154f987f4dc0fe0dd0feedac9e473aa4ba8 # v1.286.0
-        with:
-          ruby-version: '3.4'
-
-      - name: Install html-proofer
-        run: |
-          gem install nokogiri --version 1.18.6 --no-document -- --use-system-libraries
-          gem install html-proofer --version 5.0.10 --no-document -- --use-system-libraries
-        env:
-          NOKOGIRI_USE_SYSTEM_LIBRARIES: "true"
-
-      # Comes from https://github.com/gjtorikian/html-proofer?tab=readme-ov-file#caching-with-continuous-integration
-      - name: Cache HTMLProofer
-        uses: actions/cache@8b402f58fbc84540c8b491a91e594a4576fec3d7 # v5.0.2
-        with:
-          path: tmp/.htmlproofer
-          key: ${{ runner.os }}-htmlproofer
-
-      - name: Verify
-        run: ./docs/scripts/verify.sh docs/site