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

src/safety_manager.h

@@ -0,0 +1,51 @@
+/**
+ * @file safety_manager.h
+ * @brief Safety Manager — Hill-Hold + Auto-Apply Logik.
+ *
+ * @arch SWA-001
+ * @reqs SWE-007 SWE-008 SWE-009 SWE-010
+ *
+ * ASIL: D.
+ *
+ * State Machine:
+ *   IDLE  --(engine_off & v<0.5)--> AUTO_APPLY_ARMED
+ *   AUTO_APPLY_ARMED --(40 * 50ms = 2s)--> AUTO_APPLY_TRIGGERED
+ *   AUTO_APPLY_TRIGGERED --(state==APPLIED)--> IDLE
+ *
+ *   IDLE  --(grade>5% & v<0.5 & brake)--> HILL_HOLD_ARMED
+ *   HILL_HOLD_ARMED --(!brake)--> HILL_HOLD_ACTIVE
+ *   HILL_HOLD_ACTIVE --(v>2 km/h | state==APPLIED)--> IDLE
+ */
+#ifndef SAFETY_MANAGER_H
+#define SAFETY_MANAGER_H
+
+#include "epb_types.h"
+
+typedef enum {
+    SAFETY_IDLE                 = 0,
+    SAFETY_HILL_HOLD_ARMED      = 1,
+    SAFETY_HILL_HOLD_ACTIVE     = 2,
+    SAFETY_AUTO_APPLY_ARMED     = 3,
+    SAFETY_AUTO_APPLY_TRIGGERED = 4
+} SafetyState;
+
+typedef struct {
+    bool     engine_running;
+    bool     brake_pedal_pressed;
+    float    vehicle_speed_kmh;
+    float    grade_percent;
+    EpbState current_state;       /* aus Apply Controller */
+} SafetyInputs;
+
+/* Schwellwerte als Konstanten, damit Tests darauf zugreifen koennen. */
+#define SAFETY_AUTO_APPLY_DELAY_50MS  40U   /* 40 * 50ms = 2.0 s */
+#define SAFETY_STANDSTILL_KMH         0.5f
+#define SAFETY_RELEASE_KMH            2.0f
+#define SAFETY_HILLHOLD_GRADE_PCT     5.0f
+
+EpbStatus   safety_mgr_init(void);
+void        safety_mgr_step_50ms(const SafetyInputs* in);
+bool        safety_mgr_apply_requested(void);
+SafetyState safety_mgr_get_state(void);
+
+#endif /* SAFETY_MANAGER_H */