feat(backend): add editor context, draft flow bootstrap, and draft summary endpoints

add backend endpoints for editor context and draft summaries

ensure draft flow bootstrap for editor-driven workflows
improve draft-aware initialization and summary reads for clients

backend/app/schemas/editor.py

@@ -56,6 +56,30 @@ class DraftStructureResponse(BaseModel):
     total_groups: int
 
 
+class EditorContextResponse(BaseModel):
+    scheme_id: str
+    current_scheme_version_id: str
+    current_version_number: int
+    scheme_status: str
+    scheme_version_status: str
+    editor_available: bool
+    current_is_draft: bool
+    create_draft_available: bool
+    recommended_action: str
+
+
+class DraftSummaryResponse(BaseModel):
+    scheme_id: str
+    scheme_version_id: str
+    status: str
+    total_seats: int
+    total_sectors: int
+    total_groups: int
+    validation_summary: dict
+    structure_diff_summary: dict
+    publish_readiness: dict
+
+
 class SeatPatchRequest(BaseModel):
     seat_id: str | None = Field(default=None, max_length=128)
     sector_id: str | None = Field(default=None, max_length=128)