ci: split reusable workflow into lint + e2e jobs

- Run ruff in a dedicated lint job (faster feedback)
- Keep e2e separate and install dependencies only there
- Force Playwright Chromium install to avoid cache-related missing binaries
- Trigger CI on PRs and pushes to main

https://chatgpt.com/share/694ae842-1588-800f-9418-31e7d02ac45e

.github/workflows/ci.yml

@@ -1,12 +1,11 @@
-name: CI
+name: ci
 
 on:
-  push:
   pull_request:
+  push:
+    branches:
+      - main
 
 jobs:
-  test:
+  tests:
     uses: ./.github/workflows/reusable-test.yml
-    with:
-      python-version: "3.12"
-      matomo-token-description: "ci-token"