Simplify annotation vote to yes/no/can't-tell (ladder UI preserved on branch ladder-voting)

app.py

@@ -303,7 +303,7 @@ _start_bucket_flusher()
 class Annotation(BaseModel):
     seed_id: int
     code: str
-    verdict: str  # "depth" | "none" | "skip"
+    verdict: str  # simple ui: "yes" | "no" | "skip"; ladder ui: "depth" | "none" | "skip"
     depth_index: int | None = None  # 0-based rung index when verdict == "depth"
     rung_code: str | None = None
     ladder_index: int | None = None  # which ':'-part, for composite codes
@@ -311,6 +311,7 @@ class Annotation(BaseModel):
     gt: bool | None = None
     judge: str | None = None
     session: str = ""
+    ui: str | None = None  # "simple-v1" | "ladder-v1" — distinguishes the two voting UIs
 
 
 app = Server()