refactor(models): unify primary model rotation and sync

Refactor the model management page so every primary-model entry point goes through setPrimary(). This centralizes fallback-chain rotation, removes stale/deleted models from fallbacks, deduplicates the chain, and refreshes both the default bar and provider cards after primary changes.

src/pages/models.js

@@ -299,18 +299,10 @@ function bindWaterfallActions(page, state) {
   container.querySelectorAll('.btn-set-primary-from-fb').forEach(btn => {
     btn.onclick = () => {
       const full = btn.dataset.id
-      const oldPrimary = getCurrentPrimary(state.config)
-      const fallbacks = state.config.agents.defaults.model.fallbacks || []
-
       pushUndo(state)
-      // 1. 设置新主模型
       setPrimary(state, full)
-      // 2. 将旧主模型放入备选链（原位置或末尾）
-      const newFallbacks = fallbacks.filter(f => f !== full)
-      if (oldPrimary) newFallbacks.push(oldPrimary)
-      state.config.agents.defaults.model.fallbacks = newFallbacks
-
       renderDefaultBar(page, state)
+      renderProviders(page, state)
       updateUndoBtn(page, state)
       autoSave(state)
       toast(t('models.setAsPrimarySuccess', { model: full }), 'success')
@@ -1003,9 +995,39 @@ async function handleAction(action, btn, card, section, providerKey, provider, p
   }
 }
 
-// 设置主模型(仅修改 state,不写入文件)
+// 设置主模型入口
 function setPrimary(state, full) {
+  const oldPrimary = getCurrentPrimary(state.config)
+  if (oldPrimary === full) return
+
+  // 1. 设置新主模型状态
   ensureDefaultModelConfig(state).primary = full
+
+  // 2. 轮转备选链状态
+  rotateFallbackChain(state, oldPrimary, full)
+}
+
+// 处理主模型变更后，备选链的数据流转
+function rotateFallbackChain(state, oldPrimary, newPrimary) {
+  const modelConfig = ensureDefaultModelConfig(state)
+  const validModels = new Set(collectAllModels(state.config).map(m => m.full))
+  const seen = new Set()
+
+  // 从备选链中移除新上位的主模型
+  const newFallbacks = (modelConfig.fallbacks || [])
+    .filter(f => f !== newPrimary && validModels.has(f))
+    .filter(f => {
+      if (seen.has(f)) return false
+      seen.add(f)
+      return true
+    })
+
+  // 将原主模型降级放入备选链
+  if (oldPrimary && oldPrimary !== newPrimary && validModels.has(oldPrimary) && !seen.has(oldPrimary)) {
+    newFallbacks.push(oldPrimary)
+  }
+
+  modelConfig.fallbacks = newFallbacks
 }
 
 // 应用默认模型:primary + 其余自动成为备选