[P3] modal-warn-wraps-on-phone: the unsaved-changes warning can wrap and grow the pinned strip

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

.modal-warn is an unbounded flex item in a strip that carries flex-wrap: wrap. At phone width, "You have unsaved changes." plus OK plus "Discard changes?" can wrap to a second line, making the pinned strip a line taller and eating scrollport on exactly the narrow case the pin exists to serve.

No committed capture has the warning present at phone width: 27c-elevator-schedule-unsaved runs at the scene's default (desktop) viewport, so nothing would catch this.

Fix when picked up: give the warning min-width: 0 with truncation, or budget an explicit two-line allowance so the strip's height is intentional rather than incidental. Add a phone-width capture with the dialog dirty. Consider scoping the class to .modal-actions > .modal-warn at the same time, since margin-right: auto is currently global.

/bmad-code-review.

Start with the pinned dialog footer and the .modal-warn and .modal-actions > .modal-warn styles mentioned in the issue. Run the 27c-elevator-schedule-unsaved capture, then add a phone-width run with the dialog dirty; done means the warning does not cause unintended wrapping or strip growth.