Stop a stationary pointer from pinning the menu selection

A pointer parked over a menu row re-claimed the selection on every frame's
declaration, so keyboard navigation fought the mouse sixty times a second
and lost -- press Up, and the hover put the selection straight back. Found
by the UI demo's scripted tour: its mouse click leaves the pointer resting
on the menu, and the Up keystroke that followed did nothing.

Hover now moves the selection only on frames the pointer actually moved (or
clicked), through a frame-latched motion edge beside the existing press
edge. Parking the mouse claims nothing; moving it onto a row still selects,
clicking still selects and activates. Regression test drives the exact
sequence: click a row, move the selection away by keyboard, redeclare, and
assert the stationary pointer stole nothing back.

Co-Authored-By: Claude Code (Claude Fable 5, claude-fable-5) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01KzBDV2fqgnUAcqCKqKvc71

include/akgl/ui.h

@@ -425,8 +425,11 @@ akerr_ErrorContext AKERR_NOIGNORE *akgl_ui_label(char *id, char *text, akgl_UiAn
  * @brief Declare a vertical menu from caller-owned state, centred on screen.
  *
  * One row per entry, the selected row drawn inverted (ink on fill swaps to
- * fill on ink). Hovering a row with the mouse moves `selected` to it; a left
- * click on a row sets `activated`. Keyboard and gamepad go through
+ * fill on ink). Moving the mouse onto a row selects it; a left click on a
+ * row selects and sets `activated`. A *stationary* pointer claims nothing --
+ * parking the mouse over the menu must not pin the selection against the
+ * keyboard, which is fighting sixty times a second and losing. Keyboard and
+ * gamepad go through
  * akgl_ui_menu_handle_event(), which the application calls for whichever
  * menu currently has its attention -- that routing *is* the focus model.
  * Legal only between akgl_ui_frame_begin() and akgl_ui_frame_end().