ci: run the verify workflow on main only, not on every branch

Drop the pull_request trigger from CI so the heavy verify job (format,
lint, typecheck, test, build, rust:check, Playwright e2e) runs only on
push to main. Add workflow_dispatch so it can still be triggered by hand
on a branch when needed.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

Author: yousef20920

.github/workflows/ci.yml

@@ -1,10 +1,10 @@
 name: CI
 
 on:
-  pull_request:
   push:
     branches:
       - main
+  workflow_dispatch:
 
 permissions:
   contents: read