feat: add ASCII art email signature and update documentation

- Add signature.txt with stylish VALKNAR banner and contact info
- Update README.md to document the new signature file
- Clean up .gitignore to track signature.txt
- Remove legacy config files (prettier, rubocop, pre-commit, etc.)
- Update arty.yml with additional installation scripts

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

signature.txt

@@ -0,0 +1,10 @@
+
+      ██╗   ██╗ █████╗ ██╗     ██╗  ██╗███╗   ██╗ █████╗ ██████╗
+      ██║   ██║██╔══██╗██║     ██║ ██╔╝████╗  ██║██╔══██╗██╔══██╗
+      ██║   ██║███████║██║     █████╔╝ ██╔██╗ ██║███████║██████╔╝
+      ╚██╗ ██╔╝██╔══██║██║     ██╔═██╗ ██║╚██╗██║██╔══██║██╔══██╗
+       ╚████╔╝ ██║  ██║███████╗██║  ██╗██║ ╚████║██║  ██║██║  ██║
+        ╚═══╝  ╚═╝  ╚═╝╚══════╝╚═╝  ╚═╝╚═╝  ╚═══╝╚═╝  ╚═╝╚═╝  ╚═╝
+  ───────────────────────────────────────────────────────────────────
+   valknar@pivoine.art  │  (+49) 174 8188918  │  https://pivoine.art
+  ───────────────────────────────────────────────────────────────────