fix(ci): pin pnpm version in Actions (no root package.json to read)

pnpm/action-setup ran with no version: `uses:` steps ignore
defaults.run.working-directory, so it executed at the repo root, which has no
package.json (per-app monorepo) → "No pnpm version specified". Pin version: 9
explicitly. Also drop setup-node's `cache: pnpm` — the act_runner cache server
isn't reachable from the DinD job containers, and the install is fast anyway.

.gitea/workflows/ci.yml

@@ -25,13 +25,16 @@ jobs:
     steps:
       - uses: actions/checkout@v4
 
+      # `uses:` steps ignore defaults.run.working-directory, so action-setup runs
+      # at the repo root — which has no package.json (per-app monorepo). Pin the
+      # version explicitly instead of reading packageManager.
       - uses: pnpm/action-setup@v4
+        with:
+          version: 9
 
       - uses: actions/setup-node@v4
         with:
           node-version: 22
-          cache: pnpm
-          cache-dependency-path: ${{ matrix.target.dir }}/pnpm-lock.yaml
 
       - name: Install
         run: pnpm install --frozen-lockfile
@@ -47,11 +50,11 @@ jobs:
     steps:
       - uses: actions/checkout@v4
       - uses: pnpm/action-setup@v4
+        with:
+          version: 9
       - uses: actions/setup-node@v4
         with:
           node-version: 22
-          cache: pnpm
-          cache-dependency-path: services/platform-api/pnpm-lock.yaml
       - name: Install
         run: pnpm install --frozen-lockfile
       - name: Test