fix: load .env without python-dotenv when package is missing

Co-authored-by: Cursor <cursoragent@cursor.com>

app.py

@@ -3,7 +3,6 @@ import secrets
 from pathlib import Path
 from typing import Optional
 
-from dotenv import load_dotenv
 from flask import Flask, flash, redirect, render_template, request, url_for
 from flask_login import LoginManager, current_user, login_required, login_user, logout_user
 from flask_wtf.csrf import CSRFProtect
@@ -11,9 +10,45 @@ from flask_wtf.csrf import CSRFProtect
 from forms import GroupForm, LoginForm, ServiceForm
 from models import Service, ServiceGroup, User, db
 
-# 与 app.py 同目录的 .env；若文件不存在则忽略。已存在于操作系统中的同名变量不会被覆盖。
 _ROOT = Path(__file__).resolve().parent
-load_dotenv(_ROOT / ".env")
+
+
+def _load_env_file(path: Path) -> None:
+    """若未安装 python-dotenv，用最小实现加载 .env（不覆盖已有环境变量）。"""
+    if not path.is_file():
+        return
+    try:
+        raw = path.read_text(encoding="utf-8-sig")
+    except OSError:
+        return
+    for line in raw.splitlines():
+        s = line.strip()
+        if not s or s.startswith("#"):
+            continue
+        if s.lower().startswith("export "):
+            s = s[7:].lstrip()
+        if "=" not in s:
+            continue
+        key, _, rest = s.partition("=")
+        key = key.strip()
+        if not key:
+            continue
+        val = rest.strip()
+        if len(val) >= 2 and val[0] == val[-1] and val[0] in "\"'":
+            val = val[1:-1]
+        if key not in os.environ:
+            os.environ[key] = val
+
+
+try:
+    from dotenv import load_dotenv as _dotenv_load
+except ImportError:
+    _dotenv_load = None
+
+if _dotenv_load:
+    _dotenv_load(_ROOT / ".env")
+else:
+    _load_env_file(_ROOT / ".env")
 
 login_manager = LoginManager()
 csrf = CSRFProtect()