Implement BotPredictVisiblePosition and expose via botlib API

[themuffinator]

Motivation

• Restore the missing movement perception helper by implementing BotPredictVisiblePosition to match the Quake III flow.
• Enable callers to obtain a reachable point that is visible from a goal for navigation/aiming decisions.
• Reuse existing AAS reachability and trace utilities to compute visibility along movement paths.

Description

• Implemented BotPredictVisiblePosition in src/botlib/ai_move/bot_move.c, which iteratively queries reachabilities with BotGetReachabilityToGoal and tests visibility against reach.start/reach.end.
• Added a local line-of-sight helper BotMove_Visible that uses Q2_Trace with CONTENTS_SOLID|CONTENTS_PLAYERCLIP to test visibility.
• Declared the new prototype in src/botlib/ai_move/bot_move.h and added the API entry to src/q2bridge/botlib.h.
• Wired the function into the export table by adding BotInterface_BotPredictVisiblePosition and setting exportTable.BotPredictVisiblePosition in src/botlib/interface/bot_interface.c.

Testing

• No automated tests were executed for this change.
• The changes were committed locally with the message Implement BotPredictVisiblePosition.

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Codex Task