feat(docs): migrate Phase 1 files to Diataxis structure
Move 21 files to new locations:
- Tutorials: quick-start guides, agent creation guide
- How-To: installation, customization, workflows
- Explanation: core concepts, features, game-dev, builder
- Reference: merged glossary from BMM and BMGD
Also:
- Copy images to new locations
- Update internal links via migration script (73 links updated)
- Build verified successfully
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Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
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