feat(i18n): tools + landing page + doorstop generator in English

Phase 1 of full English translation:
- generate_doorstop_items.py: all 55 items (SG/SYS/SWE/SA/SWA) rewritten in English
- generate_landing_page.py: full UI labels, KPI cards, section headings in English
- traceability.py: docstring, error messages, HTML headers in English
- generate_test_report.py: report content + table headers in English
- All 55 markdown items in safety/sg/, reqs/, arch/ regenerated in English

Still to come:
- demo-epb filled Word docs (PID, plans, safety, manuals, audit artefacts)
- Code comments + test names + CI workflow step names
- README + dev-process repo templates

reqs/swe/SWE-020.md

@@ -1,7 +1,7 @@
 ---
 active: true
 derived: false
-header: 'LED-Steuerung'
+header: 'LED control'
 level: 1.20
 normative: true
 reviewed: null
@@ -10,6 +10,6 @@ links:
 asil: QM
 ---
 
-# SWE-020: LED-Steuerung
+# SWE-020: LED control
 
-Apply-aktiv: LED dauerleuchtend. Release: LED aus. Fehler: LED blinkt 4 Hz. Service-Mode: LED blinkt 2 Hz.
+Apply active: LED solid. Release: LED off. Fault: LED blinks at 4 Hz. Service mode: LED blinks at 2 Hz.