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

Makefile

@@ -13,10 +13,12 @@ BUILD    = build
 
 SRCS    = $(SRC_DIR)/switch_debouncer.c \
           $(SRC_DIR)/actuator_driver.c \
-          $(SRC_DIR)/apply_controller.c
+          $(SRC_DIR)/apply_controller.c \
+          $(SRC_DIR)/safety_manager.c
 OBJS    = $(SRCS:%.c=$(BUILD)/%.o)
 
-TESTS   = test_switch_debouncer test_actuator_driver test_apply_controller
+TESTS   = test_switch_debouncer test_actuator_driver test_apply_controller \
+          test_safety_manager
 TEST_BINS = $(TESTS:%=$(BUILD)/%)
 
 .PHONY: all test coverage clean misra static