Add capture pane functionality

[max-legrand]

My attempt at adding #57

Amp threads:
https://ampcode.com/threads/T-019b299e-2bbd-76c6-96f8-90b628790215
https://ampcode.com/threads/T-019b29bd-8c39-750b-a626-2122ade62abc
https://ampcode.com/threads/T-019b29bd-8c39-750b-a626-2122ade62abc

[rockorager]

Thanks for working on this! Capture pane is a useful feature (issue #57).

However, I think the implementation conflates two separate concerns:

1. Capturing the pane content - the core feature
2. Opening in an editor - one specific use case

Issues with current approach

1. Timeout is fragile

prise.set_timeout(500, function()

This waits 500ms hoping the server responded and client wrote the file. Large scrollbacks could take longer, or it could be unnecessarily slow for small ones.

2. Should be event-driven

Instead of a timeout, the client should emit an event when the capture is complete:

{ type = "capture_pane_complete", path = "/tmp/...", content = "..." }

Then Lua handles it reactively.

3. Editor logic shouldn't be baked in

The PR hardcodes opening $EDITOR in a new tab with auto-close. This is one specific workflow, but users might want to:

• Pipe to fzf/grep
• Send to clipboard
• Open in a floating window
• Append to a log file
• etc.

Suggested approach

Make capture_pane a simple primitive:

• pty:capture_pane() triggers capture
• Client emits event when complete: { type = "capture_pane_complete", pty_id = ..., content = "..." }
• User handles the event in their config however they want

The "open in editor" workflow can be a documented example in the README showing how to wire it up, not built into the core.

This keeps the API composable and lets users build their own workflows on top of the primitive.

[max-legrand]

Unsure exactly when I'll be able to address the feedback on this (or #60). If these are sitting for a while and it is quicker for someone else to make the necessary changes to get this merged I'm more than happy to close this PR out in favor of having the changes be included sooner, but I will try to find the time to make changes based on the review comments.