Implement BotPredictVisiblePosition and export wiring

[themuffinator]

Motivation

• Restore movement perception parity by implementing BotPredictVisiblePosition as referenced in the Quake III parity matrix to unblock combat navigation/aiming.
• Provide a helper to predict a reachable position that is visible from a goal using existing AAS reachability and trace utilities.
• Expose the new functionality through the bot interface/export table so callers (game/engine) can access the prediction.

Description

• Implemented BotPredictVisiblePosition in src/botlib/ai_move/bot_move.c, which steps reachabilities toward a goal and uses a trace-based visibility check to pick the best visible point, and added the helper BotMove_VisiblePosition for line-of-sight checks.
• Declared the new API in src/botlib/ai_move/bot_move.h as BotPredictVisiblePosition.
• Added a wrapper BotInterface_BotPredictVisiblePosition in src/botlib/interface/bot_interface.c and wired it into the exported bot table as BotPredictVisiblePosition.
• Added the export slot to src/q2bridge/botlib.h so the function is available via the bridge/import/exports table.

Testing

• No automated tests were executed as part of this change.
• A local build/test was not performed in this rollout (no automated build/test run reported).

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Codex Task