Persist .next/cache across deploys for faster rebuilds

Each deploy creates a fresh worktree and deletes .next, losing the
Turbopack build cache. Now restore .next/cache from the live site
into the stage before pnpm build, so Next.js can do incremental
compilation. After cutover the cache persists in the live .next/ for
the next deploy.

.gitea/workflows/deploy.yaml

@@ -299,6 +299,13 @@ jobs:
           find . -maxdepth 3 -name '*.tsbuildinfo' -delete 2>/dev/null || true
           rm -rf .output dist .next .next/types .next/dev
 
+          # Restore build cache from last deploy so Turbopack can do
+          # incremental compilation (much faster rebuilds).
+          if [ -d "${LIVE}/.next/cache" ]; then
+            mkdir -p .next/cache
+            cp -r "${LIVE}/.next/cache/." .next/cache/
+          fi
+
           # Stage shares MySQL with the live app + emulator. Keep the stage pool
           # tiny so install/test/build cannot exhaust max_connections.
           export DATABASE_POOL_SIZE="${DEPLOY_DATABASE_POOL_SIZE:-5}"