feat: Safety Manager + Traceability + PlantUML in CI

- Implement Safety Manager (SWA-001, ASIL-D): Hill-Hold + Auto-Apply
  state machine, 13 unit tests
- Update SWA-002 + SWA-001 link coverage so all SWE reqs are covered
- New tool: tools/traceability.py — Markdown-frontmatter-basierter
  Traceability-Checker + HTML/JSON-Matrix-Generator (Doorstop-Format ohne
  Doorstop-Dependency)
- New tool: tools/render_plantuml.py — extrahiert PlantUML-Bloecke aus
  arch/**.md und rendert via plantuml.com zu SVG
- validate.yml: neue Steps Traceability-Check, Matrix-Publish, PlantUML-
  Render; uploaded als Gitea-Artefakte

arch/swe/SWA-001.md

@@ -10,6 +10,8 @@ links:
   - SWE-008
   - SWE-009
   - SWE-010
+  - SWE-011
+  - SWE-012
 asil: D
 ---
 

arch/swe/SWA-002.md

@@ -10,6 +10,7 @@ links:
   - SWE-002
   - SWE-003
   - SWE-004
+  - SWE-005
 asil: D
 ---