Review German geometry-error docs, translate to English, rebuild site

German docs (docs/de):
- Fix broken shell cross-links (missing R_ prefix), missing .md, old
  wiki path, and wrong/missing #vertex anchors
- Fix error/check codes: CONCECUTIVE->CONSECUTIVE, C_ prefix on
  collapsed-to-line check, GS_S_->GE_S_ typo, correct requirement-ID
  and expected-result cells
- Fix German spelling/grammar and remove stray English fragments
- Unify headings/labels, remove stray <br /> lines
- Repoint all figure links from external GitLab URLs to local img/

English docs (docs/en):
- Translate all 21 R_GE_* detail files from the wiki-pointer stubs,
  preserving IDs, codes, links, images and tables verbatim
- Fix CONCECUTIVE->CONSECUTIVE in geometric.md

Rebuild both mkdocs sites into public/de and public/en.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>