fix(android): lime flash on double-tap auto-move confirmation

When handle_double_tap recognises a double-tap and fires MoveRequestEvent,
the moved card(s) are immediately tinted STATE_SUCCESS (lime #acc267) with
a 0.35 s HintHighlight so the player sees visual confirmation before the
card animation begins.

- Priority 1 (single top card): flashes that card only.
- Priority 2 (whole face-up stack): flashes every card in drag.cards.

Reuses the existing tick_hint_highlight cleanup path (restores sprite
to WHITE when timer expires) so no new system or component is needed.
The flash duration (0.35 s) slightly outlasts a typical card animation
(~0.3 s), giving the tint a brief moment at the destination before clearing.

Marks P1 "Double-tap auto-move visible feedback" as closed in
PLAYABILITY_TODO (hardware trigger-verification still manual).

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

docs/android/PLAYABILITY_TODO.md

@@ -95,9 +95,15 @@ rewrites required.
   the `Layout` struct; `card_plugin::card_positions` and
   `input_plugin::card_position` / `pile_drop_rect` read from the struct
   so rendering and hit-testing stay in sync across viewport sizes.
-- [ ] **Double-tap auto-move visible feedback.** `handle_double_tap`
-  exists since `395a322` — verify it triggers on hardware and add a
-  brief source-card flash / highlight to confirm to the user.
+- [x] **Double-tap auto-move visible feedback.** *Closed 2026-05-11.*
+  On a recognised double-tap (priority 1 single-card or priority 2
+  stack move), the moved card(s) receive a 0.35 s lime flash
+  (`STATE_SUCCESS` tint + `HintHighlight { remaining: 0.35 }`) before
+  the move request is written. The flash persists through the card
+  animation and is cleaned up by the existing `tick_hint_highlight`
+  system. Hardware trigger-verification remains a manual step — connect
+  AVD or device and confirm two rapid `TouchPhase::Ended` events within
+  0.5 s produce the lime flash.
 
 ## P2 — Polish