Implement BotReachabilityArea and expose it in the botlib move API

[themuffinator]

Motivation

• Restore movement/AAS parity by adding the missing reachability-area lookup used by movement and goal code.
• Match HLIL/Quake logic for handling solid/mover surfaces, water detection, and origin→area resolution so other move helpers can rely on consistent area semantics.
• Export the helper through the botlib interface so the game DLL and other subsystems can call into the move layer.

Description

• Implemented BotReachabilityArea in src/botlib/ai_move/bot_move.c with mover handling, water/solid checks, and a fallback fuzzy area resolver (BotMove_FuzzyPointReachabilityArea).
• Added internal helpers BotMove_AreaHasReachability and BotMove_GetClientBounds to check area reachability and obtain client bounding boxes for traces.
• Declared the symbol in the move header by adding int BotReachabilityArea(const vec3_t origin, int client); to src/botlib/ai_move/bot_move.h.
• Exposed the function through the botlib export table by adding BotInterface_BotReachabilityArea and wiring exportTable.BotReachabilityArea in src/botlib/interface/bot_interface.c, and added the prototype to src/q2bridge/botlib.h so the game can call it.

Testing

• No automated tests were executed for this change.
• Basic repository operations used during development included targeted searches and source edits, and the changes were committed to the working branch.

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Codex Task