feat(user): enhance email handling with validation and normalization functions

- Introduced `looksLikePlausibleEmail` to validate email format, ensuring only plausible addresses are processed.
- Added `normalizeEmailCandidate` to standardize email input, returning null for invalid formats.
- Updated `decodeEncryptedBlob` to utilize normalization functions for both UTF-8 and hex formats, improving email decryption reliability.
- Adjusted `SettingsService` to ensure email is set after merging adult access state, maintaining data integrity.

backend/models/community/user.js

@@ -8,6 +8,26 @@ function encodeEncryptedValueToBlob(value) {
     return Buffer.from(encrypted, 'utf8');
 }
 
+/** Nur echte Adressen zurückgeben — verhindert Anzeige von Base64-/Key-artigem Müll bei fehlender Entschlüsselung. */
+function looksLikePlausibleEmail(s) {
+    if (typeof s !== 'string') {
+        return false;
+    }
+    const t = s.trim();
+    if (!t || t.length > 254) {
+        return false;
+    }
+    return /^[^\s@]+@[^\s@]+\.[^\s@]{2,}$/i.test(t);
+}
+
+function normalizeEmailCandidate(s) {
+    if (!s || typeof s !== 'string') {
+        return null;
+    }
+    const t = s.trim();
+    return looksLikePlausibleEmail(t) ? t : null;
+}
+
 function decodeEncryptedBlob(value) {
     if (!value) {
         return null;
@@ -16,8 +36,9 @@ function decodeEncryptedBlob(value) {
     try {
         const encryptedUtf8 = value.toString('utf8');
         const decryptedUtf8 = decrypt(encryptedUtf8);
-        if (decryptedUtf8) {
-            return decryptedUtf8;
+        const fromUtf8 = normalizeEmailCandidate(decryptedUtf8);
+        if (fromUtf8) {
+            return fromUtf8;
         }
     } catch (error) {
         console.warn('Email utf8 decryption failed, trying legacy hex format:', error.message);
@@ -26,15 +47,16 @@ function decodeEncryptedBlob(value) {
     try {
         const encryptedHex = value.toString('hex');
         const decryptedHex = decrypt(encryptedHex);
-        if (decryptedHex) {
-            return decryptedHex;
+        const fromHex = normalizeEmailCandidate(decryptedHex);
+        if (fromHex) {
+            return fromHex;
         }
     } catch (error) {
         console.warn('Email legacy hex decryption failed:', error.message);
     }
 
     try {
-        return value.toString('utf8');
+        return normalizeEmailCandidate(value.toString('utf8'));
     } catch (error) {
         console.warn('Email could not be read as plain text:', error.message);
         return null;