feat(models): 组织、用户、角色、客户、会话与消息模型

按组织边界定义数据关系，补齐仓储层与通用工具，迁移脚本可重复执行。

backend/app/utils/urls.py

@@ -0,0 +1,40 @@
+"""
+Copyright 2024-2026 ChatterMate
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+"""
+
+import re
+
+# Any scheme prefix, matched case-insensitively so "HTTP://" can't sneak past
+# scheme checks or get a second scheme prepended.
+_SCHEME_RE = re.compile(r"^([a-zA-Z][a-zA-Z0-9+.-]*)://")
+
+
+def normalize_url(value: str, require_https: bool = False) -> str:
+    """Normalize a user-supplied URL: default the scheme to https and lowercase
+    an existing scheme. Raises ValueError for blank input, non-http(s) schemes,
+    and — when require_https is set — plain http URLs.
+    """
+    value = value.strip()
+    if not value:
+        raise ValueError("URL must not be blank")
+    match = _SCHEME_RE.match(value)
+    if match:
+        scheme = match.group(1).lower()
+        if scheme not in ("http", "https"):
+            raise ValueError("URL must use http or https")
+        if require_https and scheme != "https":
+            raise ValueError("URL must use https")
+        return f"{scheme}://{value[match.end():]}"
+    return f"https://{value}"