docs: add VitePress documentation site with i18n and GitHub Pages deployment

- Set up VitePress with bilingual support (Chinese root + English /en/)
- Create unified sidebar navigation with all doc sections
- Add custom Anthropic brand theme (#D97757)
- Create Quick Start pages (zh/en) from README content
- Migrate 7 .en.md files to docs/en/ directory structure
- Translate memory/agent/skills docs to English (9 files)
- Generate English-only architecture diagrams (11 images via PicTactic)
- Copy English-ready images for agent/skills sections (21 images)
- Configure custom domain (claudecodehaha.relakkesyang.org)
- Localize Chinese UI labels (sidebar, outline, footer)
- Add documentation site badge to READMEs
- Fix dead links and update cross-references for VitePress

Co-Authored-By: Claude Opus 4.6 (1M context) <[email protected]>

docs/.vitepress/theme/custom.css

@@ -0,0 +1,14 @@
+:root {
+  --vp-c-brand-1: #D97757;
+  --vp-c-brand-2: #c5684a;
+  --vp-c-brand-3: #b15a3e;
+  --vp-c-brand-soft: rgba(217, 119, 87, 0.14);
+  --vp-sidebar-width: 280px;
+}
+
+.dark {
+  --vp-c-brand-1: #D97757;
+  --vp-c-brand-2: #e08868;
+  --vp-c-brand-3: #ea9a7a;
+  --vp-c-brand-soft: rgba(217, 119, 87, 0.16);
+}