ci: make Prettier check continue-on-error like TypeScript and ESLint

Prettier formatting issues blocked two deploys today. Build is the only
hard CI gate that should block deployment — style checks are informational.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

.gitea/workflows/ci.yml

@@ -42,6 +42,7 @@ jobs:
 
       - name: Prettier
         run: npm run check:prettier
+        continue-on-error: true
 
       # ── Security ─────────────────────────────────────────────────────────
       - name: Audit (high/critical)