build: 打通 FastAPI 与 Vue 最小工程、依赖与数据库连接

后端入口、配置、Redis 与 Alembic 迁移就位；前端 Vite 工程可安装可构建。

backend/app/core/external_urls.py

@@ -0,0 +1,29 @@
+"""
+Copyright 2024-2026 ReplyPier
+
+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.
+"""
+
+# Base URLs of the third-party APIs the channel and CRM adapters call.
+#
+# Deployments never set these. The e2e suite points them at its recording fake
+# (e2e/services/fake-externals) so channel journeys run end to end without
+# reaching Telegram, Meta, Slack, … Read once at import, which is also when the
+# adapters bind them (Meta's helpers take the base as a default argument).
+
+import os
+
+
+def external_base(env_var: str, default: str) -> str:
+    """`default`, unless `env_var` overrides it; never with a trailing slash."""
+    return (os.getenv(env_var) or default).rstrip("/")