docs: add banner SVG and badges to README files

- Add assets/banner.svg (visual header for GitHub repo page)
- Update README.md and README.de.md with banner image and Python/License/Platform badges
- Update .gitignore to exclude LOCK*.txt and machine-specific README variants

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: Lukas Geiger

.gitignore

@@ -47,6 +47,11 @@ TODO.md
 DECISIONS.md
 HANDOFF-CODEX-START.md
 CODEX-AUTO-DEBUG-DESIGN.md
+LOCK*.txt
+
+# --- Machine-specific README variants (merged into main READMEs) ---
+README-ASUS-GEI.md
+README.de-ASUS-GEI.md
 
 # --- Interne Steuerungsdateien ---
 PORTIERUNGSPLAN.md