Clean up repo: prune non-dev assets, redirect build output, add .gitignore

- Remove old/unneeded material: mockups/, docs/Image (ChatGPT imgs·GIFs),
  character art docs (IMAGE_GEN_*, *.md.old, BRAND_CHARACTERS, CHARACTER_PROFILES),
  asset backups (Characters_OriginalBackup, SourceCandidates),
  unused puppet variants (LeeSoriExtended/Regenerated/Upper/V2/V3), tools/ art scripts
- Keep active assets only: LeeSori + LeeSoriDance puppets, Live2DPreview, Live2DHost, mascot PNGs
- Fix dangling references in kept docs (README, CLAUDE, ARCHITECTURE, TYPOGRAPHY, CHARACTER_UI_INTEGRATION)
- Refresh HANDOFF.md to live state (LeeSoriDance puppet, D:\Project paths)
- Redirect all build output to Build/ via Directory.Build.props (bin+obj)
- Add .gitignore and untrack previously committed bin/obj artifacts

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

docs/ARCHITECTURE.md

@@ -11,7 +11,7 @@
 | AI | **Anthropic REST (HttpClient)** 또는 `Anthropic.SDK` NuGet | 구조화 출력(tool use) |
 | 패키징 | **MSIX 또는 velopack/single-file** | 배포. 라이선스 제외 옵션과 연동 |
 
-> WPF-UI가 Mica 배경 + Fluent 컨트롤 + 다크테마를 제공해 목업(`mockups/main_window.html`)의
+> WPF-UI가 Mica 배경 + Fluent 컨트롤 + 다크테마를 제공해 다크·Fluent
 > 룩앤필을 네이티브로 재현할 수 있다. 그래프는 LiveCharts2의 `CartesianChart`로 로그 X축(주파수)
 > + 선형 Y축(dB), 영역 그라데이션 채우기.