Refactor MainController to use DataHelper and catch SQLException

[G30RG3-GJ]

Refactored loadBookInfo2 in MainController to use a new DataHelper.getIssueDetails method.
This change:

1. Prevents SQL injection by using PreparedStatement.
2. Catches specific SQLException instead of generic Exception in MainController.
3. Propagates exceptions from DataHelper to MainController for better error handling.
4. Adds unit tests for the new DataHelper method.

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PR created automatically by Jules for task 725577877229468235 started by @G30RG3-GJ

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