Redesigns the waypoint list panel to match the drone-status/missions
panels: no title bar, close button floats over the tab row, tabs get
more vertical padding.
Removes the "Fetch wind" and "Validate" header buttons along with the
now-fully-orphaned WindValidatePanel screen and its WindService
support code (fetchValidation, WindValidationResult and friends) -
nothing else referenced them.
Wind is now fetched automatically instead: HeaderWindNotifier gains
ensurePerWaypointWind(), called when the waypoint list panel opens and
when the header pill's per-waypoint toggle switches on. A lat/lon
signature of the waypoint list tracks whether the fetched data is
still current, so a ref.listen(currentMissionProvider) in the same
notifier refetches only when the list itself changes (position added/
removed/moved) - not on every altitude/speed edit. Waypoints that
already carry wind data (e.g. loaded from a saved mission) short-
circuit the check instead of re-fetching pointlessly.
Also wires per-waypoint wind markers into the fly-mode map, which
never had them (plan_screen.dart built windMarkers; fly_screen.dart
just never did) - the reported "doesn't work in fly mode" bug.
windMarkerWidth() moved from a plan_screen.dart-private method to
wind_marker_pill.dart so both screens can share it.
Test containers in widget_test.dart now override windServiceProvider
with a MockClient so the new auto-fetch trigger can't reach the real
network during tests.