Menu card: odometer-style digit roll on value updates

[tangentlin]

Motivation

The menu card (src/menu-card/card.ts) currently snaps straight to new values when its data signature changes. A small "slot machine" digit-roll animation on update would give the card a more alive, tactile feel without touching its information density.

Proposal

When today/30d figures change between renders, animate the digits rolling from the old value to the new one (each digit column ticks independently) instead of an instant swap.

Feasibility notes

• card.ts is a pure Canvas 2D draw function invoked by MenuCardRenderer and cached by data signature (TrayManager.refreshCard). True animation requires a short-lived requestAnimationFrame loop in the hidden card window while a transition is in flight, then handing the final PNG frame back to the tray — a scoped change to menu-card-window.ts's render contract (currently one-shot draw → PNG).
• Menu items only display a static bitmap per open, so the practical animation window is: kick off the roll when new data arrives, capture a few interim frames, and let it settle before the menu is next opened (or accept it's only visible if the menu happens to be open across a refresh).

Acceptance criteria

• Digit-roll transition plays when todayCost/cost30d/etc. change from a previously-rendered value.
• No animation (instant render) on first paint or when values are unchanged, matching current caching behavior.
• No added flicker/redraw cost when the menu is closed.