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>

.gitignore

@@ -0,0 +1,30 @@
+# ── 빌드 산출물 (git과 분리) ─────────────────────────────
+# 모든 빌드 결과물은 Directory.Build.props에 의해 이 폴더로 모인다.
+/Build/
+
+# 혹시 프로젝트 폴더에 생성되는 기본 bin/obj (안전망)
+[Bb]in/
+[Oo]bj/
+
+# ── Visual Studio / Rider / VS Code ─────────────────────
+.vs/
+.vscode/
+*.user
+*.suo
+*.userosscache
+*.sln.docstates
+*_i.c
+*_p.c
+
+# ── .NET / MSBuild 부산물 ───────────────────────────────
+project.lock.json
+project.assets.json
+*.nuget.props
+*.nuget.targets
+msbuild.log
+*.binlog
+
+# ── OS ──────────────────────────────────────────────────
+Thumbs.db
+Desktop.ini
+.DS_Store