Restructure backend into microservices, add envelope encryption, DM files, and message editing

backend/services/main/validation.py

@@ -0,0 +1,26 @@
+import re
+
+def is_valid_username(username: str) -> bool:
+    if len(username) < 3 or len(username) > 20:
+        return False
+    # Only allow English letters, numbers, dashes and underscores
+    if not re.match(r'^[a-zA-Z0-9_-]+$', username):
+        return False
+    return True
+
+
+def is_valid_display_name(display_name: str) -> bool:
+    if len(display_name) < 1 or len(display_name) > 64:
+        return False
+    # Check if not blank (only whitespace)
+    if not display_name.strip():
+        return False
+    return True
+
+
+def is_valid_password(password: str) -> bool:
+    if len(password) < 5 or len(password) > 50:
+        return False
+    if re.search(r'[\s\u180E\u200B-\u200D\u2060\uFEFF]', password):
+        return False
+    return True