```

docs: restructure AI modes guide and add ChatGPT browser companion docs

- Rewrite ai-modes-guide.html with task-oriented structure covering all AI
  features: cohost, ChatGPT browser source, primary chat bot, private bot,
  processing tools (moderation, translation, RAG, summaries), and overlay builder
- Clarify distinction between SSN cohost sessions and ChatGPT website companion
  mode with setup steps for the experimental browser source integration
- Update guides.html navigation to reflect new AI guide organization
- Expand common fixes with ChatGPT browser source and cohost troubleshooting

Note: "Fix Kick gift capture" mentioned in original message not visible in
provided diff (may be in truncated portion or separate commit).
```

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