fix(richtlinien): improve examples, copy, and Wikipedia link

- Rule cards now show before→after examples; strikethrough rule input
  renders with CSS line-through so the visual context is honest
- Illegible-words rule shows output only — can't represent unreadable
  text as readable characters
- Intro drops fictional family names in favour of "egal wer tippt"
- Wikipedia card copy is more direct; link uses icon instead of
  parenthetical "(öffnet in neuem Tab)" text

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

frontend/messages/en.json

@@ -827,9 +827,9 @@
 	"transcription_mode_help_body": "Read shows the transcription as flowing text. Edit opens the text fields for each passage.",
 
 	"richtlinien_title": "Transcription Guidelines",
-	"richtlinien_intro": "So every letter is transcribed consistently — whether Tante Hedwig or Cousin Paul is typing — here are our rules. The page grows with us: as soon as we agree a new convention, it lands here.",
-	"richtlinien_wiki_text": "You don't need the full Kurrent and Sütterlin alphabet on this page — that's what Wikipedia is for. Here are our own rules for everything Wikipedia can't answer.",
-	"richtlinien_wiki_link": "Wikipedia →",
+	"richtlinien_intro": "So every letter is transcribed consistently — no matter who types — here are our rules. The page grows with us: as soon as we agree a new convention, it lands here.",
+	"richtlinien_wiki_text": "The Kurrent and Sütterlin alphabets are well explained on Wikipedia. Here you'll only find our own conventions for this archive.",
+	"richtlinien_wiki_link": "Wikipedia",
 	"richtlinien_rules_label": "Transcription rules",
 	"richtlinien_rule_unleserlich_title": "Illegible words",
 	"richtlinien_rule_unleserlich_body": "If you can't decipher a word even after trying, write [unleserlich]. Someone else will take another look later.",