ci: npm install --include=optional so Sharp platform binary installs

The runner omits optional deps, dropping @img/sharp-linux-x64 (sharps own
optional platform package). --include=optional forces it back in.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

.gitea/workflows/deploy.yml

@@ -16,10 +16,11 @@ jobs:
         with:
           node-version: 22
 
-      # npm (not bun) so Sharp's native binary for astro:assets image
-      # optimization installs reliably on the runner
+      # npm (not bun) + --include=optional so Sharp's platform binary
+      # (@img/sharp-linux-x64, an optional dep) installs on the runner,
+      # which otherwise omits optional deps -> astro:assets MissingSharp
       - name: Install dependencies
-        run: npm install
+        run: npm install --include=optional
 
       - name: Build site
         run: npm run build