Use SSH deploy key instead of account token for theme submodule

Avoids tying CI to a personal/bot Gitea account: the same DEPLOY_SSH_KEY
secret used for the webserver rsync step is reused as a read-only Gitea
deploy key on hmk/pelican-latex. The submodule's tracked HTTPS URL is
overridden to SSH just for this checkout so it authenticates with that
key instead of needing a token with access to both repos.

.gitea/workflows/build-deploy.yml

@@ -15,14 +15,31 @@ jobs:
           apt-get update
           apt-get install -y --no-install-recommends git rsync openssh-client nodejs
 
-      - name: Checkout (incl. theme submodule)
+      - name: Checkout
         uses: actions/checkout@v4
         with:
-          submodules: recursive
-          # Default job token only covers this repo; the theme submodule
-          # (hmk/pelican-latex) is a separate private repo, so a token with
-          # read access to both is needed here.
-          token: ${{ secrets.CHECKOUT_TOKEN }}
+          submodules: false
+
+      - name: Set up SSH key
+        # Same key used both as the theme repo's deploy key (Gitea) and for
+        # the webserver login (below) — one secret, two authorized_keys entries.
+        env:
+          DEPLOY_SSH_KEY: ${{ secrets.DEPLOY_SSH_KEY }}
+          DEPLOY_HOST: ${{ secrets.DEPLOY_HOST }}
+        run: |
+          mkdir -p ~/.ssh
+          printf '%s\n' "$DEPLOY_SSH_KEY" > ~/.ssh/deploy_key
+          chmod 600 ~/.ssh/deploy_key
+          ssh-keyscan -H git.haemka.in "$DEPLOY_HOST" >> ~/.ssh/known_hosts 2>/dev/null
+
+      - name: Fetch theme submodule
+        run: |
+          # Override the submodule's tracked HTTPS URL for this checkout only,
+          # so it's fetched over SSH with the deploy key instead of needing a
+          # token with access to both repos.
+          git config submodule.themes/latex.url git@git.haemka.in:hmk/pelican-latex.git
+          GIT_SSH_COMMAND="ssh -i ~/.ssh/deploy_key -o StrictHostKeyChecking=yes" \
+            git submodule update --init --recursive
 
       - name: Install Python dependencies
         run: pip install --no-cache-dir -r requirements.txt
@@ -35,12 +52,7 @@ jobs:
           DEPLOY_HOST: ${{ secrets.DEPLOY_HOST }}
           DEPLOY_USER: ${{ secrets.DEPLOY_USER }}
           DEPLOY_PATH: ${{ secrets.DEPLOY_PATH }}
-          DEPLOY_SSH_KEY: ${{ secrets.DEPLOY_SSH_KEY }}
         run: |
-          mkdir -p ~/.ssh
-          printf '%s\n' "$DEPLOY_SSH_KEY" > ~/.ssh/deploy_key
-          chmod 600 ~/.ssh/deploy_key
-          ssh-keyscan -H "$DEPLOY_HOST" >> ~/.ssh/known_hosts 2>/dev/null
           rsync -avz --delete \
             -e "ssh -i ~/.ssh/deploy_key -o StrictHostKeyChecking=yes" \
             output/ "${DEPLOY_USER}@${DEPLOY_HOST}:${DEPLOY_PATH}"