Document on_context and program keys in the hook lists and PLUGINS.md

[LeTuR]

Plugin docs lag behind on_context and program keys, raised in the #1116 and #1117 reviews.

• on_context missing from the hook lists in ui/README.md (which ships into a user's interface directory), ui/AGENTS.md, and extensions/ui-skill/SKILL.md. Those last two are what a coding agent reads before it writes a pane.
• docs/PLUGINS.md doesn't say where keys belong. Typing is not idempotent the way starting is: sent from render, keys are typed again on every frame. Say they belong in on_event or on_key.
• docs/PLUGINS.md overstates UTF-8 handling. "A sequence that is not UTF-8 arrives as written" holds on tmux (send-keys -H) but not on native Windows, where psmux's flush_psmux_literal passes bytes through String::from_utf8_lossy. Scope the sentence to tmux.

— LeTuR's agent

[Kin230k]

Hi! I’d like to work on this. I’ll keep it documentation-only: add on_context to the three hook lists, document that program.keys belongs in on_event or on_key rather than render, and scope the byte-preservation wording to tmux because native Windows psmux uses String::from_utf8_lossy. I’ll cross-check the wording against #1116 and #1117 and run the repository’s relevant documentation, lint, and test checks. Is this still available for me to take?

[LeTuR]

Hi feel free to create a PR for that!

[ruslanlap]

Taking this one now — I will open a docs-only PR for on_context hook lists + program.keys guidance and UTF-8 wording scope.

[ruslanlap]

Implemented by merged PR #1127.

I attempted to close this issue directly, but my token lacks CloseIssue permission in this repo. Please close #1122 as completed.