feat: 平台配置表扩展配图/字数字段，微信公众号正文插入配图，合规检查从DB读规则

- PlatformConfig模型新增requires_image、image_count_min/max、image_width/height、min_words/max_words
- schemas.py同步PlatformConfigBase/Create/Update/Response新字段
- initial_data.py为三大平台填充初始值（微信需配图、字数800-1500等）
- database.py添加新列ALTER TABLE迁移
- platforms.html重写编辑弹窗（正确字段名+配图/字数设置）
- writer.py微信公众号文章正文h1后插入<img>占位
- compliance_checker.py接受platform_config参数，从DB读取规则替代硬编码
- compliance_optimizer.py启动时加载DB平台配置传入checker

platform/backend/app/initial_data.py

@@ -81,11 +81,18 @@ def import_initial_data():
                     "icon": "🔍",
                     "default_format": "长文深度分析，1500-3000字，有数据支撑",
                     "compliance_rules": {
-                        "max_length": 50000,
-                        "requires_authentication": False,
-                        "sensitive_words": ["敏感词示例1", "敏感词示例2"]
+                        "max_title_len": 100,
+                        "allowed_tags": ["科技", "生活", "职场", "教育", "可持续", "AI", "远程工作", "个人成长"],
+                        "forbidden_patterns": ["加微信", "私聊", "付费咨询", "点击领取"]
                     },
-                    "is_active": True
+                    "is_active": True,
+                    "requires_image": False,
+                    "image_count_min": 0,
+                    "image_count_max": 0,
+                    "image_width": 0,
+                    "image_height": 0,
+                    "min_words": 1500,
+                    "max_words": 3000
                 },
                 {
                     "platform": "wechat",
@@ -93,10 +100,18 @@ def import_initial_data():
                     "icon": "💚",
                     "default_format": "公众号图文，800-1500字，亲切口语化",
                     "compliance_rules": {
-                        "max_length": 20000,
-                        "requires_authentication": True
+                        "max_title_len": 32,
+                        "allowed_tags": ["科技", "生活", "职场", "教育", "可持续", "AI", "远程工作", "个人成长"],
+                        "forbidden_patterns": ["诱导分享", "朋友圈", "转发群"]
                     },
-                    "is_active": True
+                    "is_active": True,
+                    "requires_image": True,
+                    "image_count_min": 1,
+                    "image_count_max": 3,
+                    "image_width": 1080,
+                    "image_height": 1080,
+                    "min_words": 800,
+                    "max_words": 1500
                 },
                 {
                     "platform": "xiaohongshu",
@@ -104,11 +119,18 @@ def import_initial_data():
                     "icon": "📕",
                     "default_format": "图文笔记，300-800字，emoji+标签",
                     "compliance_rules": {
-                        "max_length": 1000,
-                        "requires_tags": True,
-                        "max_tags": 10
+                        "max_title_len": 50,
+                        "allowed_tags": ["生活方式", "可持续", "AI", "个人成长", "极简", "环保"],
+                        "forbidden_patterns": ["私信", "加群", "导流"]
                     },
-                    "is_active": True
+                    "is_active": True,
+                    "requires_image": True,
+                    "image_count_min": 3,
+                    "image_count_max": 6,
+                    "image_width": 1080,
+                    "image_height": 1440,
+                    "min_words": 300,
+                    "max_words": 800
                 }
             ]
             for p in platforms: