Allow re-sign workflow to trigger CI via manual workflow dispatch

[foxfirecodes]

Motivation

• Enable the re-sign commits workflow to re-run CI on the rewritten signed commit by invoking the CI workflow directly.
• Provide context to CI runs dispatched outside of standard PR pushes by adding workflow_dispatch inputs so the origin can be recorded.

Description

• Add workflow_dispatch to .github/workflows/ci.yml with source and pr inputs so the CI workflow can be manually dispatched with metadata.
• Grant actions: write permission in resign-pr-commits.yml and add a step that uses gh api to POST to actions/workflows/ci.yml/dispatches to trigger CI on the signed branch, passing inputs[source]=resign-commits and inputs[pr].
• Keep existing re-sign logic that rebases and re-signs commits and push the rewritten branch before triggering CI.

Testing

• No automated tests were executed as part of this change because the modifications are limited to GitHub Actions workflow definitions.

---

Codex Task