mecatui: bound /effort picker at constrained terminal heights #2170

Scope

Bound the selectable tier rows in cmd/mecatui/ui/effort.go within the offered conversation-region height. The fixed six-tier picker currently renders every row regardless of height; on short terminals the card can overflow and the selected tier can be off-screen. This is a small, independent bounded.List candidate even though the tier vocabulary is fixed.

Required outcome

• Budget the title, optional no-reasoning warning, footer hints, card frame, and overflow indicators before sizing the list. Keep the selected tier visible as the user moves through the six tiers, including when opening on max in a short viewport. Provide an explicit compact fallback when the frame and controls cannot fit.
• Keep ● current separate from cursor selection; use stable tier IDs and the shared presentListRow helper for standard selectable rows. Preserve the existing live key hints, idle/capability gating, auto → empty wire value, and direct fork-resume on Enter.
• Do not fold in bug: selecting auto reasoning effort inherits the previous override #1485 (the separate auto-effort override bug) or change /models.

Verification

Add scenario-first coverage for short-height clipping, cursor reveal and endpoint navigation, optional warning geometry, compact fallback, normal-height presentation, and selection/close behavior through the real UI state. Run focused Effort/UI and bounded tests before project gates.

Relates to #1742 and #1589.