NavigationWorld: add navmesh pathfinding with Recast & Detour

[Tron-xR]

Add full navmesh support to the engine:

3rdparty:

• Vendor Recast & Detour (MIT license) for navmesh generation and pathfinding
• Vendor DetourCrowd for agent management and crowd simulation

Build system (scripts/):

• recastnavigation.lua: Genie build script for Recast/Detour/DetourCrowd
• genie.lua: register recastnavigation build target
• crown.lua: add recastnavigation includes and link dependency

NavigationWorld (src/world/):

• navigation_world.h/cpp: new sub-world managing navmesh loading, pathfinding (find_path, nearest_point, ray_cast, random_point), agent creation/destruction/target/state, and crowd simulation
• Integrated into World: created/destroyed/updated each frame
• navigation_agent component routed through create_components

Navmesh resource (src/resource/):

• navmesh_resource.h/cpp: new .navmesh resource type with data compiler
• data_compiler.cpp: register navmesh compiler + RESOURCE_TYPE extern
• resource/types.h: add RESOURCE_TYPE_NAVMESH / RESOURCE_VERSION_NAVMESH
• device.cpp: register navmesh runtime resource type (simple_resource)

Lua API (src/lua/):

• lua_stack.h/inl: add NavigationWorld getter with marker check
• lua_api.cpp: expose NavigationWorld methods (find_path, nearest_point, ray_cast, random_point, agent_create/destroy/set_target/position/velocity)
• World:navigation_world() getter in Lua

[dbartolini]

This PR does not even compile. If it is a work in progress, you should mark it as a draft. If you plan to work seriously on this, it should at least include a dedicated example in the samples folder, and minimal tooling to generate navmeshes for levels inside the editor.