Refactor AI summarizer client initialization to include MongoDB manager and add statistics endpoint

- Updated `InitAISummarizerClient` to accept `mongoManager` for tracking translation success.
- Introduced new `Statistics` endpoint in the dashboard to fetch scraping and translation statistics.
- Enhanced `TranslationWorker` to utilize the new success counter for tracking successful translations.
- Added necessary data structures and query forms for statistics reporting.

This refactor improves the tracking of AI translation success and provides new insights through the dashboard statistics.

internal/dashboard/form.go

@@ -27,3 +27,8 @@ type RecentQuery struct {
 	Limit  int    `query:"limit"`
 	Cursor string `query:"cursor"`
 }
+
+// StatisticsQuery binds query params for GET /dashboard/statistics.
+type StatisticsQuery struct {
+	Days int `query:"days"`
+}