Add executive authority model, mission_executor BT layer, and enforce executive gating in trajectory_manager

[varadVaidya]

Motivation

• Introduce a clear executive boundary so mission logic cannot bypass vehicle-level safety and authorization decisions.
• Separate mission/application concerns (behavior trees) from executive responsibilities to simplify guarantees about what may command motion.
• Make manager lifecycle on_configure() non-blocking by removing deterministic startup sleep/gates to avoid brittle launch-order dependencies.

Description

• Add executive contract fields to peregrine_interfaces::msg::UAVState (fault_latched, motion_authorized, takeoff_authorized, landing_authorized, executive_reason) and a new service peregrine_interfaces::srv::ClearEmergency to explicitly clear latched emergencies.
• Implement executive semantics in uav_manager: compute and publish the new uav_state fields in publishUavState(), expose clear_emergency service, and remove forwarding of generic motion actions (go_to/execute_trajectory) from the executive.
• Add trajectory_manager executive gate (executive_gate.hpp) and subscription to uav_state, and enforce policy at goal acceptance and during execution (reject goals when executive denies motion, abort active goals when authority is revoked, and forbid takeoff/land via the generic execute_trajectory action).
• Remove blocking startup/topic-discovery waits and <thread> sleeps from estimation_manager, trajectory_manager, and control_manager on_configure() implementations and replace with non-blocking lifecycle activation behavior and comments clarifying responsibilities.
• Add a new mission_executor package implementing a BehaviorTree-based mission application layer with a reusable example tree and launch integration in peregrine_bringup.
• Update documentation (ARCHITECTURE.md, package READMEs) to reflect the layered separation (mission/executive/motion) and executive gating rules.
• Add unit tests for the executive gate (trajectory_manager/test_executive_gate.cpp) and update trajectory_manager CMake to run the test, plus add/adjust uav_manager unit tests related to emergency behavior.

Testing

• Ran ament/unit tests: trajectory_manager::ExecutiveGateTest (3 cases) executed and passed.
• Ran uav_manager supervisor unit tests (including emergency/clear behavior) and they passed.
• Full workspace build and test (colcon/ament) performed locally; build and the added tests completed successfully.

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Codex Task