Add workflow_dispatch trigger to CI

Allows manually triggering a run to test the CI workflow (e.g. the new
scheduled job) without waiting for the weekly cron.

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

Author: sis0k0

.github/workflows/ci.yml

@@ -4,6 +4,7 @@ on:
   push:
     branches: ["main"]
   pull_request:
+  workflow_dispatch:
   schedule:
     - cron: '0 6 * * 1'