Add BotAddAvoidSpot and export via bot interface

[themuffinator]

Motivation

• Implement the missing BotAddAvoidSpot API to match the Quake III/Parity matrix requirement and restore avoid-spot lifecycle behavior.
• Preserve AVOID_CLEAR semantics and radius/type behavior so move logic can clear or append avoid spots as in the original implementation.
• Ensure the function is callable from the external botlib export table so game code can register avoid spots for move states.

Description

• Add the declaration void BotAddAvoidSpot(int movestate, vec3_t origin, float radius, int type); to src/botlib/ai_move/bot_move.h.
• Implement BotAddAvoidSpot in src/botlib/ai_move/bot_move.c with a commented header and logic to clear on AVOID_CLEAR, append until MAX_AVOIDSPOTS, and store origin, radius, and type.
• Add a wrapper BotInterface_BotAddAvoidSpot in src/botlib/interface/bot_interface.c and export it via exportTable.BotAddAvoidSpot so the function is exposed through the bot API.
• Update src/q2bridge/botlib.h to include the BotAddAvoidSpot function pointer in the bridge/export struct.

Testing

• No automated tests were executed for this change.

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Codex Task