Snake 0.9: crown control via scroll-delta turns (firmware-derived)

docs/CROWN.md

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+# Crown control experiment (v0.9)
+
+Firmware study of the O63 OTA (`upd_miwear.watch.o63.zip`) found how the crown
+reaches quickapps: there is **no crown/rotary JS event** (no `onCrown`,
+`onRotary`, wheel keyevents in `vela_quickapp.bin`), but the native layer
+(`vela_ap.bin`, `inputmanager/lv_touchpad_wheel_interface.c` + the
+`crown_scroll` input tag in `lvx_inputmanager.c`) routes crown rotation into
+**scroll deltas of the focused scrollable container**.
+
+So Snake listens to the crown indirectly:
+
+- the page is wrapped in a full-screen vertical `scroll` component with the
+  dial centered inside it,
+- `onscroll` fires for both crown rotation and finger scroll,
+- the page converts each scroll delta into a **queued 90° turn**
+  (`snake.rotateDir`, already in the codebase): positive delta =
+  clockwise, negative = counterclockwise, `CROWN_STEP_PX` px of scroll per
+  turn,
+- because turns are 90° relative steps, the crown always turns the snake
+  left/right regardless of where the head is pointing, and reversals are
+  structurally impossible (rotateDir never emits a 180° flip),
+- the scroll position is actively re-centered (`scrollTo({ top: center })`)
+  after each event so the board never visually moves; only the idle-swipe
+  fallback path (when no scroll events arrive, e.g. some firmwares coalesce
+  crown scroll with the swipe handler) uses `onswipe` as before,
+- swipes still work exactly as in 0.8; both input paths feed the same
+  two-slot turn queue.
+
+Open questions that need the physical watch:
+
+- does the Crown S4 emit scroll deltas with sign, and at what px granularity?
+- does `onscroll` fire for crown motion at all on this firmware, or only for
+  touch scroll? If not, the `CROWN_STEP_PX` accumulator still catches the
+  swipe-path fallback but true crown control would need native access.