feat(backend): add publish readiness contract and guarded publish flow

add backend readiness contract for publish prechecks

guard publish flow with explicit validation and version-aware checks
make publish behavior more predictable for clients and safer against stale state

backend/app/schemas/publish_readiness.py

@@ -1,15 +1,12 @@
+from __future__ import annotations
+
 from pydantic import BaseModel
 
 
-class PublishReadinessValidationSummary(BaseModel):
-    sectors_count: int
-    groups_count: int
-    seats_count: int
-    priced_seats_count: int
-    unpriced_seats_count: int
-    duplicate_seat_ids_count: int
-    seats_with_missing_contract_count: int
-    is_publishable: bool
+class PublishReadinessSnapshot(BaseModel):
+    available: bool
+    categories_count: int
+    rules_count: int
 
 
 class PublishReadinessPricingCoverage(BaseModel):
@@ -19,12 +16,6 @@ class PublishReadinessPricingCoverage(BaseModel):
     coverage_percent: float
 
 
-class PublishReadinessSnapshot(BaseModel):
-    available: bool
-    categories_count: int
-    rules_count: int
-
-
 class PublishReadinessFlags(BaseModel):
     validation_publishable: bool
     snapshot_available: bool
@@ -38,17 +29,17 @@ class PublishReadinessResponse(BaseModel):
     scheme_id: str
     scheme_version_id: str
     status: str
-    validation_summary: PublishReadinessValidationSummary
+    validation_summary: dict
     pricing_coverage: PublishReadinessPricingCoverage
     snapshot: PublishReadinessSnapshot
     readiness: PublishReadinessFlags
 
 
-class SchemePublishActionResponse(BaseModel):
+class PublishExecutionResponse(BaseModel):
     scheme_id: str
     scheme_version_id: str
     status: str
     current_version_number: int
     published_at: str | None
     pricing_snapshot: dict
-    validation_summary: PublishReadinessValidationSummary
+    validation_summary: dict