feat: add demand page modules and admin endpoints

Add full backend support for a demand request page, including:
- New database models for demand hero, feature cards, form configuration, and product recommendations
- Alembic migration for the new tables
- Default seed data for demand page components
- Public site config endpoint exposing demand data
- Admin CRUD operations and configuration for demand modules
- Extended lead query filters for source page, keyword, and date range
- Updated Pydantic schemas for lead query parameters
- Comprehensive test coverage for all new endpoints

app/content.py

@@ -120,6 +120,41 @@ VEHICLE_OPTIONS = [
     },
 ]
 
+DEMAND_HERO = [
+    {
+        "kicker": "3步定制",
+        "title": "告诉我们日期、人数和想法",
+        "description": "管家会按同行人、预算和体力强度，重新组合酒店、用车和景点节奏。",
+        "steps": ["提交需求", "管家沟通", "确认方案"],
+    }
+]
+
+DEMAND_FEATURE_CARDS = [
+    {"title": "动线", "description": "按天数顺路排"},
+    {"title": "住宿", "description": "城市与山野组合"},
+    {"title": "用车", "description": "人数行李匹配"},
+]
+
+DEMAND_FORM = {
+    "destinationLabel": "目的地/玩法",
+    "destinationPlaceholder": "例如：贵州、黄果树、西江苗寨",
+    "phoneLabel": "联系方式",
+    "phonePlaceholder": "手机号 / 微信号",
+    "noteLabel": "补充说明",
+    "notePlaceholder": "出行日期、人数、酒店偏好、预算范围",
+    "submitLabel": "提交出行需求",
+    "chips": ["贵州", "黄果树", "荔波小七孔", "西江苗寨", "梵净山", "万峰林"],
+}
+
+DEMAND_RECOMMENDATIONS = [
+    {
+        "title": "热门推荐",
+        "subtitle": "也可以先挑一条线路沟通",
+        "start": 16,
+        "end": 22,
+    }
+]
+
 CAMPAIGNS = [
     {"slug": "classic-deal", "title": "经典打卡特惠", "start": 0, "end": 8, "coverImage": HERO_SLIDES[0]["image"]},
     {"slug": "outdoor-deal", "title": "山野野咖特惠", "start": 8, "end": 16, "coverImage": HERO_SLIDES[1]["image"]},