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/components/onboarding/StepAiFeatures.tsx

@@ -75,7 +75,7 @@ export function StepAiFeatures() {
                 The AI tagger model labels images so you can search with{" "}
                 <code className="rounded bg-gray-900 px-1 py-0.5 text-[11px] text-gray-200 light-theme:bg-gray-800 light-theme:text-gray-100">/t</code> — tags look like:
               </p>
-              <div className="mt-3 flex flex-wrap items-center gap-1 rounded-lg border border-white/[0.07] p-0.5 light-theme:border-gray-300/80">
+              <div className="mt-3 inline-flex max-w-full flex-wrap items-center gap-1 rounded-lg border border-white/[0.07] p-0.5 light-theme:border-gray-300/80">
                 {(["wd", "joytag"] as const).map((model) => (
                   <TaggerModelChoice
                     key={model}