feat(i18n): full English translation of demo-epb

Phase 2 of the English translation:

Word documents (filled, EPB-specific):
- 8 plans (PID, PM, QA, SWE, Test, Project Manual, CM, RM)
- 6 safety docs (HARA, Safety Case, FMEDA, MISRA Compliance,
  Verification Report, Tool Qualification Cppcheck)
- 2 manuals (User, Service)
- 3 audit artefacts (Review minutes, NC-001, MISRA-REC-001)
- All regenerated via pandoc from English markdown sources

Code, tests, headers:
- All file headers, struct comments, function docstrings in English
- All test names (TEST_BEGIN strings) translated
- Inline comments translated
- 46 tests still green after translation

CI workflows:
- All step names in English
- Step descriptions, comments, release notes template in English

README.md fully rewritten in English with proper guided tour.

Phase 3 (still pending): dev-process repo templates + toolstack/setup docs.

Makefile

@@ -1,5 +1,5 @@
-# Makefile fuer demo-epb. Bewusst klein gehalten, damit der Demo
-# ohne externe Build-Tools (CMake, SCons) auf jedem POSIX-System baut.
+# Makefile for demo-epb. Intentionally small so the demo
+# builds on any POSIX system without external build tools (CMake, SCons).
 
 CC      ?= cc
 CFLAGS  ?= -std=c99 -Wall -Wextra -Werror -Wpedantic \