feat(backend): add publish readiness contract and pricing diagnostics

add backend readiness contract for publish prechecks

add pricing diagnostics to explain publish-blocking conditions
make publish decisions more explicit and easier to debug for clients

backend/app/schemas/publish_readiness.py

@@ -1,11 +1,54 @@
 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 PublishReadinessPricingCoverage(BaseModel):
+    total_seats: int
+    priced_seats: int
+    unpriced_seats: int
+    coverage_percent: float
+
+
+class PublishReadinessSnapshot(BaseModel):
+    available: bool
+    categories_count: int
+    rules_count: int
+
+
+class PublishReadinessFlags(BaseModel):
+    validation_publishable: bool
+    snapshot_available: bool
+    require_full_pricing_coverage: bool
+    full_pricing_coverage: bool
+    pricing_gate_passed: bool
+    is_ready_to_publish: bool
+
+
 class PublishReadinessResponse(BaseModel):
     scheme_id: str
     scheme_version_id: str
     status: str
-    validation_summary: dict
-    pricing_coverage: dict
-    snapshot: dict
-    readiness: dict
+    validation_summary: PublishReadinessValidationSummary
+    pricing_coverage: PublishReadinessPricingCoverage
+    snapshot: PublishReadinessSnapshot
+    readiness: PublishReadinessFlags
+
+
+class SchemePublishActionResponse(BaseModel):
+    scheme_id: str
+    scheme_version_id: str
+    status: str
+    current_version_number: int
+    published_at: str | None
+    pricing_snapshot: dict
+    validation_summary: PublishReadinessValidationSummary