diff: toasts show while the pane is open - #99118

Summary

TLDR: other plugins' toasts show while the /diff pane or dialog is open, where they were held until it closed

Notes

/diff opened its pane and its dialog with holdToasts: true. That option holds every transient toast while the pane is the one shown: each other plugin's $.ui.toast and the app's own, not only this plugin's. A plugin that toasts on a timer showed nothing for as long as /diff was open, and its toasts came out in a burst on close.

• The option goes from both opens. Nothing else in the mod changes, and nothing in it relied on the hold.
• Why it is safe to drop: docked, the notification row is drawn inside the transcript's column and the toast stack sits beside the dock; without the fullscreen layout a toast is one line in the footer. Neither lands between the pane and the prompt.
• One visible effect: a very long toast wraps the footer by one row while the dialog is up, as it does with no pane open. The dialog's own rows do not move.
• The README's sentence on toasts says what now happens.

Test Plan

• claude plugin test mods/diff passes: 210 pass, 0 fail
• A second plugin toasts every 1.5 s, at 80 and 120 columns, in both renderers, with /diff open for 7 s: toasts show throughout, docked and in the dialog
• The same before this change: no toast shows while /diff is open, and the held ones burst out on close
• Docked: no toast is drawn in any row of the dock
• The dialog's border and footer rows stay where they are under short toasts; a long toast grows the footer by one row

Revert-proof: 3 tests fail with the mod's hooks reverted (the mod's own suite, with the new expectations, run against the unchanged hooks)

Changelog

Fixed other plugins' toasts staying hidden while the /diff pane was open