n8n: add backend endpoints for the RAGcore Procedure Sync workflow

GET /api/v1/integrations/n8n/procedures lists every procedure Markdown
file Fleet Ops ships (all languages) with a stable per-document id and
content hash, ready for workflow 3 to push into RAGcore. POST
.../procedures-sync-result records the sync outcome as an idempotent
audit event, matching the existing return-callback/workflow-error
pattern. Extracted frontmatter parsing out of the demo knowledge
provider into a shared module so both read the same source of truth.

backend/app/schemas.py

@@ -164,6 +164,32 @@ class WorkflowErrorReportResult(BaseModel):
     occurred_at: datetime
 
 
+class ProcedureDocumentOut(BaseModel):
+    id: str
+    language: str
+    document_id: str
+    title: str
+    version: str
+    content: str
+    content_hash: str
+
+
+class ProcedureListOut(BaseModel):
+    documents: list[ProcedureDocumentOut]
+
+
+class ProcedureSyncResultIn(BaseModel):
+    execution_id: str = Field(max_length=120)
+    synced: int = Field(ge=0)
+    failed: int = Field(default=0, ge=0)
+
+
+class ProcedureSyncResultResult(BaseModel):
+    status: Literal["registered", "already_registered"]
+    execution_id: str
+    occurred_at: datetime
+
+
 class ProvideFieldsRequest(BaseModel):
     fields: dict[str, str]