CI: scope heavy jobs, build once, and remove duplicate validation work (#11570)

* CI: scope jobs and reuse build artifacts

* CI: fix scope fallback and remove unused artifact job

* CI: remove setup-node pnpm cache inputs

* CI: add pnpm store cache and dist artifact smoke

* CI: extract pnpm cache action and consume dist artifact

.github/actions/setup-pnpm-store-cache/action.yml

@@ -0,0 +1,41 @@
+name: Setup pnpm + store cache
+description: Prepare pnpm via corepack and restore pnpm store cache.
+inputs:
+  pnpm-version:
+    description: pnpm version to activate via corepack.
+    required: false
+    default: "10.23.0"
+  cache-key-suffix:
+    description: Suffix appended to the cache key.
+    required: false
+    default: "node22"
+runs:
+  using: composite
+  steps:
+    - name: Setup pnpm (corepack retry)
+      shell: bash
+      run: |
+        set -euo pipefail
+        corepack enable
+        for attempt in 1 2 3; do
+          if corepack prepare "pnpm@${{ inputs.pnpm-version }}" --activate; then
+            pnpm -v
+            exit 0
+          fi
+          echo "corepack prepare failed (attempt $attempt/3). Retrying..."
+          sleep $((attempt * 10))
+        done
+        exit 1
+
+    - name: Resolve pnpm store path
+      id: pnpm-store
+      shell: bash
+      run: echo "path=$(pnpm store path --silent)" >> "$GITHUB_OUTPUT"
+
+    - name: Restore pnpm store cache
+      uses: actions/cache@v4
+      with:
+        path: ${{ steps.pnpm-store.outputs.path }}
+        key: ${{ runner.os }}-pnpm-store-${{ inputs.cache-key-suffix }}-${{ hashFiles('pnpm-lock.yaml') }}
+        restore-keys: |
+          ${{ runner.os }}-pnpm-store-${{ inputs.cache-key-suffix }}-