feat: multi-region rule isolation — region column + config + queries

- DB: add region column to leaudit_rule_sets + leaudit_rule_type_bindings
- DB: change UNIQUE constraint from (rule_type) to (rule_type, region)
- Config: add APP_REGION to app.toml + AppSettings + __init__.pyi
- AuditServiceImpl: filter bindings by APP_REGION
- RuleServiceImpl: ListBindings/CreateBinding use APP_REGION
- Seed script: accept --region arg, tag rules by region
- OssPathUtils: BuildRuleYamlKey already accepts Region parameter

Each region can now have its own independent copy of the same rule_type,
stored in separate OSS paths and DB rows, keyed by region.

fastapi_admin/config/__init__.pyi

@@ -4,6 +4,7 @@
 APP_NAME: str
 APP_HOST: str
 APP_PORT: int
+APP_REGION: str
 APP_CORS_ORIGINS: str
 
 # JWT

fastapi_admin/config/_settings.py

@@ -19,6 +19,7 @@ class AppSettings(_Base):
     APP_NAME: str = "LeAudit Platform"
     APP_HOST: str = "0.0.0.0"
     APP_PORT: int = 8000
+    APP_REGION: str = "default"
     APP_CORS_ORIGINS: str = "*"