feat: harmonize mailbox messages

Signed-off-by: Sebastian Krupinski <krupinski01@gmail.com>

lib/Providers/MessageProperties.php

@@ -100,23 +100,27 @@ class MessageProperties extends MessagePropertiesMutableAbstract {
             }
         }
 
-        $this->data[static::PROPERTY_FLAGS] = [];
-        foreach ($message->flags() as $flag) {
-            $flag = ltrim($flag, '\\');
-            $normalized = match (strtolower($flag)) {
-                'seen' => 'seen',
-                'flagged' => 'flagged',
-                'answered' => 'answered',
-                'draft' => 'draft',
-                'deleted' => 'deleted',
-                default => strtolower($flag),
-            };
-            $this->data[static::PROPERTY_FLAGS][$normalized] = true;
-        }
+        $this->data[static::PROPERTY_FLAGS] = array_fill_keys(self::normalizeFlags($message->flags()), true);
 
         return $this;
     }
 
+    /**
+     * Normalise IMAP flags (e.g. "\\Seen", "$Forwarded") to flag names (e.g. "seen", "$forwarded").
+     *
+     * @param string[] $flags
+     * @return list<string>
+     */
+    public static function normalizeFlags(array $flags): array
+    {
+        $normalized = [];
+        foreach ($flags as $flag) {
+            $normalized[] = strtolower(ltrim($flag, '\\'));
+        }
+
+        return array_values(array_unique($normalized));
+    }
+
     // ── Cache (meta store / content store) ───────────────────────────────────
 
     /**