fix: unify backend port to 18080 and make validator targets configurable

- Set default API port to 18080 in config.py
- Add configurable validation_targets to SettingsSchema and DEFAULT_SETTINGS
- Update ValidatorService to support runtime test URL updates
- Hot-reload validation_targets from DB on startup and on settings save
- Add domestic fallback URLs (baidu.com, qq.com) to reduce foreign dependency risk
- Update Settings.vue to allow adding/removing validator target URLs in UI

app/models/schemas.py

@@ -47,6 +47,16 @@ class SettingsSchema(BaseModel):
     proxy_expiry_days: int = Field(default=7, ge=1, le=30)
     auto_validate: bool = True
     validate_interval_minutes: int = Field(default=30, ge=5, le=1440)
+    validation_targets: List[str] = Field(
+        default=[
+            "http://httpbin.org/ip",
+            "https://httpbin.org/ip",
+            "http://api.ipify.org",
+            "https://api.ipify.org",
+            "http://www.baidu.com",
+            "http://www.qq.com",
+        ]
+    )
 
 
 class CrawlResult(BaseModel):