fix(tagger): separate JoyTag confidence threshold

Store confidence thresholds per tagger model so JoyTag no longer inherits WD tuning. Refresh the active threshold when switching models, guard stale threshold saves, and keep UI Lab mocks in sync.

Also tightens the onboarding model selector so the segmented control no longer stretches across the row.

src/dev/mockBackend.ts

@@ -19,6 +19,10 @@ let nextAlbumId = 100;
 let nextTagId = 10_000;
 let mockTaggerModel: TaggerModel = db.scenario === "joytag-unready" ? "joytag" : "wd";
 let mockTaggerReady = db.scenario !== "unready" && db.scenario !== "joytag-unready";
+const mockTaggerThresholds: Record<TaggerModel, number> = {
+  wd: 0.35,
+  joytag: 0.4,
+};
 
 type AnyPayload = Record<string, any> | undefined;
 type Rgb = [number, number, number];
@@ -42,6 +46,10 @@ function isRgb(value: unknown): value is Rgb {
   return Array.isArray(value) && value.length === 3 && value.every((entry) => typeof entry === "number");
 }
 
+function isTaggerModel(value: unknown): value is TaggerModel {
+  return value === "wd" || value === "joytag";
+}
+
 function colorDistanceSq(left: Rgb, right: Rgb): number {
   return (left[0] - right[0]) ** 2 + (left[1] - right[1]) ** 2 + (left[2] - right[2]) ** 2;
 }
@@ -528,8 +536,13 @@ export async function handleMockCommand(cmd: string, payload?: unknown): Promise
     case "set_tagger_acceleration":
       return p.acceleration ?? "auto";
     case "get_tagger_threshold":
+      return mockTaggerThresholds[mockTaggerModel];
     case "set_tagger_threshold":
-      return p.threshold ?? 0.35;
+      {
+        const model = isTaggerModel(p.model) ? p.model : mockTaggerModel;
+        mockTaggerThresholds[model] = p.threshold ?? mockTaggerThresholds[model];
+        return mockTaggerThresholds[model];
+      }
     case "get_tagger_batch_size":
     case "set_tagger_batch_size":
       return p.batch_size ?? 8;