Add updateassets command with webapp code detection

- Add updateassets command to update plugin files from embedded assets
- Only include webapp assets if plugin manifest indicates webapp code presence
- Compare file contents before updating to avoid unnecessary writes
- Display count of updated files in completion message

🤖 Generated with [Claude Code](https://claude.ai/code)

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

assets/.github/workflows/ci.yml

@@ -0,0 +1,23 @@
+name: ci
+on:
+  schedule:
+    - cron: "0 0 * * *"
+  push:
+    branches:
+      - main
+    tags:
+      - "v*"
+  pull_request:
+
+permissions:
+  contents: read
+
+env:
+  IS_CI: true
+
+jobs:
+  plugin-ci:
+    uses: mattermost/actions-workflows/.github/workflows/plugin-ci.yml
+    secrets: inherit
+    with:
+      mage-version: v1.15.0