feat: Search Online (IMAP) + real Calendar/Contacts UI + iCloud auth wiring

Search Online:
- Synchronizer::searchOnline(folderId, query) virtual with default {}
- ImapSynchronizer: SELECT + UID SEARCH (Subject/From/To/TEXT) + fetch results
- MailService::searchOnline() + onlineSearchFinished/onlineSearchError signals
- MainMainWindow::onOnlineSearchRequested shows real server results

Calendar:
- Real QCalendarWidget view with per-day agenda from local mails
- New MailItemDao::findByDateRange(start, end)

Contacts:
- QTableWidget aggregating addresses from all local mails
- Regex email extraction + live search filter

iCloud/AccountService:
- Wire IcloudAuthenticator into AccountService::createAuthenticator

src/services/rulesengine.h

@@ -50,6 +50,7 @@ public:
     // Batch operations
     static int runRulesOnFolder(qint64 folderId, qint64 accountId = -1);
     static int runRulesOnMails(const QVector<qint64>& mailIds, qint64 accountId = -1);
+    static int runRulesOnSelected(const QVector<qint64>& mailIds, qint64 accountId = -1);
 
     // Callbacks for UI integration
     using ProgressCallback = std::function<void(int processed, int total, const QString& currentRule)>;