refactor(i-g): BUG-018 Pilot Split Schritt 2 — serializers+text_utils extrahiert

serializers.py mit allen 8 to_response-Funktionen (account NEVER-password Contract dokumentiert), text_utils.py mit extract_email_addresses+_strip_html als pure functions. Re-Export via noqa F401 in services.py — alle Consumer unveraendert. services.py jetzt 2786 Z. (von 3087).

Beweis: mail+sig_label_routes 51/51 passed nach ruff --fix; ruff clean.

app/plugins/builtins/mail/text_utils.py

@@ -0,0 +1,35 @@
+"""Text utilities for the Mail plugin.
+
+Extracted from services.py as part of the God-object split (BUG-018 pilot).
+Re-exported by ``app.plugins.builtins.mail.services``.
+"""
+
+from __future__ import annotations
+
+import re
+
+
+def extract_email_addresses(text: str) -> list[str]:
+    """Extract email addresses from a text string."""
+    if not text:
+        return []
+    return re.findall(r"[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\.[a-zA-Z]{2,}", text)
+
+
+def _strip_html(html: str) -> str:
+    """Simple HTML to text conversion for plain text fallback."""
+    if not html:
+        return ""
+    # Remove tags
+    text = re.sub(r"<[^>]+>", "", html)
+    # Replace HTML entities
+    text = (
+        text.replace("&nbsp;", " ")
+        .replace("&amp;", "&")
+        .replace("&lt;", "<")
+        .replace("&gt;", ">")
+        .replace("&quot;", '"')
+        .replace("&#39;", "'")
+    )
+    # Collapse whitespace
+    return re.sub(r"\s+", " ", text).strip()