feat(backend): harden draft, pricing and publish contracts

- unify typed API errors across draft, pricing and publish flows
- add stale draft and publish-state mutation guards
- add publish readiness contract and guarded publish flow
- add sellability reason codes to test seat preview
- add pricing diagnostics and strengthen snapshot/publish lifecycle consistency

backend/app/schemas/pricing_diagnostics.py

@@ -1,52 +1,55 @@
 from pydantic import BaseModel
 
 
-class PricingCoverageResponse(BaseModel):
-    scheme_id: str
-    scheme_version_id: str
-    total_seats: int
-    priced_seats: int
-    unpriced_seats: int
-    coverage_percent: float
-
-
-class UnpricedSeatItem(BaseModel):
-    seat_record_id: str
-    seat_id: str | None
-    element_id: str | None
-    sector_id: str | None
-    group_id: str | None
-    row_label: str | None
-    seat_number: str | None
-    reason_code: str
-    reason_message: str
-
-
-class UnpricedSeatListResponse(BaseModel):
-    scheme_id: str
-    scheme_version_id: str
-    total: int
-    items: list[UnpricedSeatItem]
-
-
-class ExplainMatchedRule(BaseModel):
-    matched_rule_level: str
-    matched_target_ref: str
+class PricingCategoryMutationResponse(BaseModel):
     pricing_category_id: str
+    scheme_id: str
+    name: str
+    code: str
+
+
+class PricingCategoryDeleteResponse(BaseModel):
+    deleted: bool
+    pricing_category_id: str
+
+
+class PriceRuleMutationResponse(BaseModel):
+    price_rule_id: str
+    scheme_id: str
+    pricing_category_id: str
+    target_type: str
+    target_ref: str
     amount: str
     currency: str
 
 
-class ExplainSeatPriceResponse(BaseModel):
+class PriceRuleDeleteResponse(BaseModel):
+    deleted: bool
+    price_rule_id: str
+
+
+class PricingRuleDiagnosticsItem(BaseModel):
+    price_rule_id: str
+    pricing_category_id: str
+    target_type: str
+    target_ref: str
+    amount: str
+    currency: str
+    matched_seats_count: int
+    matched_seat_ids: list[str]
+    orphan: bool
+    orphan_reason: str | None
+
+
+class PricingRuleDiagnosticsSummary(BaseModel):
+    total_rules: int
+    orphan_rules_count: int
+    active_rules_count: int
+    matched_seats_total: int
+
+
+class PricingRuleDiagnosticsResponse(BaseModel):
     scheme_id: str
     scheme_version_id: str
-    seat_id: str
-    element_id: str | None
-    sector_id: str | None
-    group_id: str | None
-    row_label: str | None
-    seat_number: str | None
-    has_price: bool
-    reason_code: str
-    reason_message: str
-    matched_rule: ExplainMatchedRule | None
+    summary: PricingRuleDiagnosticsSummary
+    items: list[PricingRuleDiagnosticsItem]