ci: Bump actions/cache to v5 and actions/download-artifact to v5

Upgrade `actions/cache/restore`, `actions/cache/save`, and
`actions/download-artifact` from v4 to v5 in composite actions.

Both v5 releases are non-breaking for our usage:
- actions/cache v5: only upgrades Node.js runtime from 20 to 24,
  no input/output changes.
- actions/download-artifact v5: the only breaking change is about
  downloads by artifact ID (nested directory behavior), which does
  not affect us since we download by name.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: mydea

.github/actions/install-playwright/action.yml

@@ -18,7 +18,7 @@ runs:
       working-directory: ${{ inputs.cwd }}
 
     - name: Restore cached playwright binaries
-      uses: actions/cache/restore@v4
+      uses: actions/cache/restore@v5
       id: playwright-cache
       with:
         path: |
@@ -43,7 +43,7 @@ runs:
 
     # Only store cache on develop branch
     - name: Store cached playwright binaries
-      uses: actions/cache/save@v4
+      uses: actions/cache/save@v5
       if: github.event_name == 'push' && github.ref == 'refs/heads/develop'
       with:
         path: |

.github/actions/restore-cache/action.yml

@@ -11,13 +11,13 @@ runs:
   steps:
     - name: Check dependency cache
       id: dep-cache
-      uses: actions/cache/restore@v4
+      uses: actions/cache/restore@v5
       with:
         path: ${{ env.CACHED_DEPENDENCY_PATHS }}
         key: ${{ inputs.dependency_cache_key }}
 
     - name: Restore build artifacts
-      uses: actions/download-artifact@v4
+      uses: actions/download-artifact@v5
       with:
         name: build-output