ci: disable pnpm cache to fix runner hangs

The single-worker Gitea runner consistently hangs when multiple parallel
jobs try to restore the pnpm cache simultaneously. Removing cache: pnpm
from setup-node trades slightly slower installs for reliable execution.

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

.gitea/workflows/ci.yml

@@ -28,7 +28,7 @@ jobs:
       - uses: actions/setup-node@v4
         with:
           node-version: 20
-          cache: pnpm
+          # no pnpm cache — concurrent cache restore hangs on single-worker runner
 
       - run: pnpm install --frozen-lockfile
 
@@ -45,7 +45,7 @@ jobs:
       - uses: actions/setup-node@v4
         with:
           node-version: 20
-          cache: pnpm
+          # no pnpm cache — concurrent cache restore hangs on single-worker runner
 
       - run: pnpm install --frozen-lockfile
 
@@ -65,7 +65,7 @@ jobs:
       - uses: actions/setup-node@v4
         with:
           node-version: 20
-          cache: pnpm
+          # no pnpm cache — concurrent cache restore hangs on single-worker runner
 
       - run: pnpm install --frozen-lockfile
 
@@ -110,7 +110,7 @@ jobs:
       - uses: actions/setup-node@v4
         with:
           node-version: 20
-          cache: pnpm
+          # no pnpm cache — concurrent cache restore hangs on single-worker runner
 
       - run: pnpm install --frozen-lockfile
 
@@ -214,7 +214,7 @@ jobs:
       - uses: actions/setup-node@v4
         with:
           node-version: 20
-          cache: pnpm
+          # no pnpm cache — concurrent cache restore hangs on single-worker runner
 
       - name: Install dependencies (hoisted for bun compile compatibility)
         run: |