fix(doctor): repair configured missing plugins

Fixes #76872.

Doctor now repairs configured-but-missing official plugins during update/doctor recovery, auto-enables the plugin after a successful repair, and preserves config when the download cannot complete. The plugin auto-enable path also honors disabled web search and only enables configured providers/channels when a manifest declares the matching capability.

Verification:
- git diff --check
- fallback-only Korean i18n check
- focused plugin auto-enable/config/doctor Vitest suite
- Crabbox published upgrade-survivor configured-plugin-installs E2E
- CI green on PR head 67ba8ac002

Co-authored-by: Jack Storment <crazycoder131@gmail.com>

ui/src/i18n/locales/ko.ts

@@ -980,7 +980,7 @@ export const ko: TranslationMap = {
         },
         isolated: {
           label: "독립 세션",
-          description: "자체 세션<EFBFBD><EFBFBD><EFBFBD>서 실행",
+          description: "자체 세션에서 실행",
         },
       },
       steps: {