[P3] schedule-esc-announcement: pressing Esc announces nothing to a screen reader

Deferred from /bmad-code-review of the pinned dialog footer (PR #664, v1.104.0). Edge Case Hunter finding.

In src/ui/templates/elevatorSchedule.ts the unsaved-changes warning renders on state.dirty, and arming the discard guard with Esc only flips its role from status to alert. The node and its text are unchanged, so nothing is announced: a live region announces content changes, not attribute changes.

A screen-reader user therefore presses Esc, has the press absorbed by the guard, and receives no feedback that anything happened. That is the same shape as the bug #664 fixed for sighted players (feedback rendered where it cannot be perceived), just on a different channel.

Fix when picked up: change the warning's text when the guard arms, so the live region has something to announce, e.g. naming the second press as the one that discards. Assert the text changes on arming rather than asserting the role attribute.

/bmad-code-review.

Start in src/ui/templates/elevatorSchedule.ts and trace the unsaved-changes warning rendered from state.dirty, including the Esc discard guard. Change the warning text when the guard arms so the live region announces that a second press will discard, then update or add the relevant assertion to verify the text changes rather than the role attribute.