Implement waypoint mission upload (MSP_SET_WP) and Fly-mode send button

Fills in MspFlightControllerLink.uploadMission(), which previously just
threw UnimplementedError, plus a new verifyMission() (both now on the
generic FlightControllerLink interface, protocol-neutral by signature -
MAVLink/ArduPilot get their own implementation later without touching
callers).

All iNAV-specific encoding lives in the new msp_waypoint_codec.dart:
- encodeMspSetWaypoint(): the 21-byte MSP_SET_WP payload. Action/P1/P2/P3
  byte layout was checked against the actual iNAV 9.1.0 source
  (navigation.c/navigation.h), not guessed - notably our generic `loiter`
  action has no configurable duration, so it maps to
  NAV_WP_ACTION_HOLD_TIME with the max representable p1 (int16 max, not
  0xFFFF - that would read as -1 and end the hold immediately instead of
  never).
- parseMspWpGetInfo(): decodes MSP_WP_GETINFO's validity/count fields,
  used by verifyMission() to confirm the FC actually accepted the full
  mission (Doku 2.2/4.5 Ready-to-Fly-Gate: "upload + verified").

uploadMission() sends one MSP_SET_WP per waypoint in order (iNAV has no
batch command - WP#1 resets the FC's mission list, every next number must
follow immediately, only the last carries NAV_WP_FLAG_LAST) and rejects
missions above NAV_MAX_WAYPOINTS upfront instead of silently truncating.
MissionSyncService now calls the real verifyMission() instead of always
confirming, throwing MissionVerificationException when the FC doesn't
confirm the mission.

FlyScreen's footer swaps the warnings button for a send button (Doku:
"ersetze den warnings button mit einem wp send button", pink horizontal
PaperPlaneIcon, matching the existing paper-plane drone iconography) -
warnings/event log stay reachable via the drone status pill's Warnings
tab. BottomStatsBar/MissionFooterBar gained onSendTap/sending in place of
the old forceShowWarningsButton.

Verified end to end on the Pixel_10a emulator: tapping send with WLAN as
the active connection type triggers the real WifiNetworkSpecifier flow
through MspFlightControllerLink (correctly reports "no devices found" -
expected, no real mLRS bridge on the emulator); the actual MSP_SET_WP/
MSP_WP_GETINFO wire behavior is covered by tests against a fake FC
responder over LoopbackTransport instead.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

app/lib/transport/msp/msp_commands.dart

@@ -14,6 +14,22 @@ abstract final class MspCommands {
   /// (`fc_msp.c`, `case MSP_RAW_GPS`)
   static const int rawGps = 106;
 
+  /// Response (4 Byte): u8 reserved, u8 maxWaypoints (NAV_MAX_WAYPOINTS),
+  /// u8 isWaypointListValid (`posControl.waypointListValid`), u8
+  /// waypointCount (`getWaypointCount()`) - Grundlage der Upload-
+  /// Verifikation (Doku 2.2/4.5: "Upload + verifiziert"), siehe
+  /// msp_waypoint_codec.dart. (`fc_msp.c`, `case MSP_WP_GETINFO`)
+  static const int wpGetInfo = 20;
+
+  /// Request-Payload (21 Byte, siehe msp_waypoint_codec.dart
+  /// `encodeMspSetWaypoint`): u8 wp_no, u8 action, i32 lat(1e-7 deg),
+  /// i32 lon(1e-7 deg), i32 alt(cm), i16 p1, i16 p2, i16 p3, u8 flag. Nur
+  /// WP#1..NAV_MAX_WAYPOINTS gueltig; WP#1 setzt die Missionsliste des FC
+  /// zurueck (neue Mission), jede weitere WP# muss exakt die naechste sein
+  /// (`fc_msp.c` `case MSP_SET_WP`, `navigation.c` `setWaypoint()` - kein
+  /// Batch-Kommando, ein Aufruf pro Wegpunkt).
+  static const int setWp = 209;
+
   /// Response: i32 estAlt(cm), i16 vario(cm/s), i32 baroAlt(cm).
   /// (`fc_msp.c`, `case MSP_ALTITUDE`)
   static const int altitude = 109;