fix: 禁用 opus[1m] 自动迁移，尊重用户手动删除 [1m] 后缀的选择

迁移逻辑过于激进，用户手动删除 [1m]] 后会被自动加回。
现在将 migrateOpusToOpus1m 改为 no-op，保留用户的手动模型选择。

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/migrations/migrateOpusToOpus1m.ts

@@ -1,43 +1,15 @@
 import { logEvent } from '../services/analytics/index.js'
-import {
-  getDefaultMainLoopModelSetting,
-  isOpus1mMergeEnabled,
-  parseUserSpecifiedModel,
-} from '../utils/model/model.js'
-import {
-  getSettingsForSource,
-  updateSettingsForSource,
-} from '../utils/settings/settings.js'
+import { isOpus1mMergeEnabled } from '../utils/model/model.js'
 
 /**
- * Migrate users with 'opus' pinned in their settings to 'opus[1m]' when they
- * are eligible for the merged Opus 1M experience (Max/Team Premium on 1P).
- *
- * CLI invocations with --model opus are unaffected: that flag is a runtime
- * override and does not touch userSettings, so it continues to use plain Opus.
- *
- * Pro subscribers are skipped — they retain separate Opus and Opus 1M options.
- * 3P users are skipped — their model strings are full model IDs, not aliases.
- *
- * Idempotent: only writes if userSettings.model is exactly 'opus'.
+ * Migration disabled: users who manually remove [1m] suffix should not
+ * have it automatically re-added. The migration was too aggressive and
+ * didn't respect user choice.
  */
 export function migrateOpusToOpus1m(): void {
+  // No-op - respect user's manual model choice
   if (!isOpus1mMergeEnabled()) {
     return
   }
-
-  const model = getSettingsForSource('userSettings')?.model
-  if (model !== 'opus') {
-    return
-  }
-
-  const migrated = 'opus[1m]'
-  const modelToSet =
-    parseUserSpecifiedModel(migrated) ===
-    parseUserSpecifiedModel(getDefaultMainLoopModelSetting())
-      ? undefined
-      : migrated
-  updateSettingsForSource('userSettings', { model: modelToSet })
-
-  logEvent('tengu_opus_to_opus1m_migration', {})
+  logEvent('tengu_opus_to_opus1m_migration', { skipped: true })
 }