feat(backend): add operational smoke tooling and safe pricing cleanup endpoints

- add backend README and refresh API map and smoke regression docs
- add full backend smoke regression script
- add admin pricing cleanup preview and dry-run endpoints
- add helper script for test pricing cleanup
- verify typed error contracts, draft flow, publish readiness and preview flows
- verify publish preview retention and clean backend startup behavior

backend/app/schemas/admin_cleanup.py

@@ -0,0 +1,51 @@
+from pydantic import BaseModel, Field
+
+
+class PricingCleanupPreviewItem(BaseModel):
+    pricing_category_id: str
+    name: str
+    code: str
+    rules_count: int = Field(ge=0)
+    matched_by: list[str]
+    deletable: bool
+
+
+class PricingCleanupPreviewResponse(BaseModel):
+    scheme_id: str
+    code_prefixes: list[str]
+    name_prefixes: list[str]
+    pricing_category_ids: list[str]
+    delete_only_without_rules: bool
+    total_candidates: int = Field(ge=0)
+    safe_to_delete_count: int = Field(ge=0)
+    items: list[PricingCleanupPreviewItem]
+
+
+class PricingCleanupExecuteRequest(BaseModel):
+    code_prefixes: list[str] = Field(default_factory=list)
+    name_prefixes: list[str] = Field(default_factory=list)
+    pricing_category_ids: list[str] = Field(default_factory=list)
+    delete_only_without_rules: bool = True
+    dry_run: bool = True
+
+
+class PricingCleanupSkippedItem(BaseModel):
+    pricing_category_id: str
+    reason: str
+
+
+class PricingCleanupExecuteResponse(BaseModel):
+    scheme_id: str
+    dry_run: bool
+    delete_only_without_rules: bool
+
+    requested_total: int = Field(ge=0)
+    matched_total: int = Field(ge=0)
+
+    would_delete_count: int = Field(ge=0)
+    deleted_count: int = Field(ge=0)
+    skipped_count: int = Field(ge=0)
+
+    would_delete_category_ids: list[str]
+    deleted_category_ids: list[str]
+    skipped: list[PricingCleanupSkippedItem]