OSC 133 / OSC 9;4 effect callbacks for libghostty-vt

[AprilNEA]

What do you want to change?

I want to add two effect callbacks to the libghostty-vt C API: OSC 133 semantic prompt marks and OSC 9;4 progress reports, following the existing pwd_changed pattern from #12956.

Why do you want to make this change?

I'm the author of expo-libghostty (https://github.com/arcboxlabs/expo-libghostty), a Ghostty terminal view for React Native / Expo that embeds libghostty-vt. On Android I cross-compile the vt static libraries myself and drive them through JNI, and I need command-finished and progress events for the mobile UI.

I acknowledge that:

• I have read the Contributing Guide and understand the contribution process.
• I have read and agree to follow the AI Usage Policy.
• I wrote this vouch request myself, in my own voice, without AI generating it.

[jcollie]

!vouch

[jcollie]

If you weren't already planning to, please submit each callback as a separate PR.