feat(backend): migrate auth and notifications off email

apps/users/email_identity.py

@@ -0,0 +1,35 @@
+from __future__ import annotations
+
+PLACEHOLDER_EMAIL_SUFFIX = "@noemail.local"
+
+
+def normalize_email_identity(value: str | None) -> str | None:
+    if value is None:
+        return None
+    normalized = value.strip().lower()
+    return normalized or None
+
+
+def normalize_mobile_number(value: str | None) -> str | None:
+    if value is None:
+        return None
+    normalized = "".join(ch for ch in value if ch.isdigit())
+    return normalized or None
+
+
+def is_valid_mobile_number(value: str | None) -> bool:
+    normalized = normalize_mobile_number(value)
+    return bool(normalized and len(normalized) == 11 and normalized.startswith("09"))
+
+
+def mask_mobile(value: str | None) -> str | None:
+    if not value:
+        return None
+    if len(value) <= 4:
+        return value
+    return f"{value[:2]}{'*' * max(len(value) - 6, 1)}{value[-4:]}"
+
+
+def is_placeholder_email(value: str | None) -> bool:
+    normalized = normalize_email_identity(value)
+    return bool(normalized and normalized.endswith(PLACEHOLDER_EMAIL_SUFFIX))