* feat: add title screen generation tooling
Add local automation for capturing WinUtil in Light and Dark themes
and generating the composite title-screen image.
* ci: automate title screen updates
Add a manual Windows workflow that compiles WinUtil, generates the
Light and Dark composite, and opens an image-only pull request.
* docs: update AGENTS.md and SPEC.md with title-screen generation details
* fix: address review comments
Tested image is correct, SHA-256 hash is identical to the previously verified output.
* fix: deselect bitmap before reading capture pixels
