chore(docs): reorganize docs/ tree + rename clawspring → cheetahclaws…

[chauncygu]

… in asset refs

Two coupled cleanups:

1. Reorganize docs/ tree. The top level had 50+ files mixed: demo gifs, logos, README localizations, comparison docs, and stub leftovers. New layout groups by kind:

   docs/
   ├── README.md (new — index page)
   ├── news.md, agent-os.md, architecture.md, contributor_guide.md
   ├── guides/, RFC/, roadmap/, superpowers/, PR/ (unchanged)
   ├── media/
   │ ├── demos/ (21 _demo.gif moved here)
   │ ├── logos/ (7 logo-.png moved here)
   │ └── screenshots/ (screenshot.png moved here)
   ├── i18n/ (7 README..MD moved here)
   └── archive/ (3 superseded docs: update_readme_v3.0.md +
   2 comparison files vs v3.03)

   Stubs removed: docs/readme.md (5 bytes, content "cheetahclaws demo") and docs/update_readme_v3.02.md (1 byte, empty).

   All moves use git mv so history is preserved.

2. Switch GitHub-absolute asset URLs to relative paths + fix lingering 'clawspring' (the project's old name) references.

   Two transformations across README.md + every doc:

   (A) Asset URLs (gif/png/md under docs/) on either repo name converted
   to file-relative paths. Survives rename and fork, works in local
   clones / IDE previews, and GitHub still renders them correctly.

       https://github.com/SafeRL-Lab/clawspring/blob/main/docs/web_demo.gif
                                              ↓
       docs/media/demos/web_demo.gif        (from README.md)
       ../media/demos/web_demo.gif          (from docs/guides/*.md)
   

   (B) Non-asset clawspring URLs (issues, DeepWiki, repo home) renamed
   to cheetahclaws but kept absolute — they're cross-repo
   identifiers, relative paths don't apply.

   Tally across 16 modified files: 0 broken refs after the pass, 0 lingering 'clawspring' references outside docs/archive/.

Tests: pre-existing suites unaffected (32/32 web_api, all green).