[AZ-652] mission_executor safety + resume + middle-waypoint (batch 9)

Geofence (INCLUSION+EXCLUSION, ≤500 ms detect→RTL), battery
thresholds (RTL@25%/land@15% + signed override), middle-waypoint
re-upload (CLEAR_ALL→upload→SET_CURRENT(0)), and post-flight
mapobjects push trigger. Adds production MAVLink command issuers
for both geofence and battery failsafe families.

Implements 6 ACs with 12 integration tests + module unit tests;
full workspace test suite green. See batch_09_cycle1_report.md
for AC coverage and known limitations.

Co-authored-by: Cursor <cursoragent@cursor.com>

crates/mission_executor/src/internal/mod.rs

@@ -1,11 +1,15 @@
 //! Internal modules for `mission_executor`. Not part of the public API.
 
+pub mod battery_thresholds;
 pub mod bit;
 pub mod bit_evaluators;
 pub mod driver;
 pub mod fixed_wing;
 pub mod fsm;
+pub mod geofence;
 pub mod lost_link;
+pub mod middle_waypoint;
 pub mod multirotor;
+pub mod post_flight;
 pub mod telemetry;
 pub mod types;