Single commit containing the entire upgrade bundle (803 files, 117623 insertions).

Components:
- yaoai-comic-studio: Spring Boot 3.3 + Java 17 backend, 16 Maven submodules
  (common, domain, security, billing, storage, ai-core, ai-providers,
   media, pipeline, agent, task, api, admin, bootstrap, worker, test)
- yaoai-admin-web: Vite 6 + Vue 3 + TypeScript + Element Plus admin console
- doc/{h5,html,miniapp}: client-side subprojects
- design-docs/: 26 Chinese PRD documents
- docs/: upgrade workflow and reference documents
- Root configs: .gitignore, .env.*, .editorconfig, .gitattributes, etc.
- 21 root-level numbered design documents (01-19 PRD)
- 3 Chinese business documents
- zhen.png and other root-level design assets

Notes: Originally 3 commits, squashed per user request (rebase -i HEAD~3). No push performed.