fix(theme): expand typography monospace fallback stack with Cascadia Code and Consolas

[ZhuchkaTriplesix]

Problem

In lib/core/theme/querya_typography.dart, the SQL editor font stack is defined solely as:

static const String mono = 'monospace';

On Windows systems, generic 'monospace' defaults to the legacy Courier New font, which lacks modern programming ligatures, proper antialiasing, and visual crispness compared to modern Windows programming fonts like Cascadia Code (Windows 11 default) and Consolas (Windows 10 default).

Proposed Solution

1. Update QueryaTypography to provide a prioritized cross-platform font family fallback list:
   • Primary: Cascadia Code (Windows 11), Consolas (Windows 10), Menlo / SF Mono (macOS), Fira Code, DejaVu Sans Mono / Ubuntu Mono (Linux), followed by fallback monospace.
2. Apply the fallback list across SQL editor styles, cell inspectors, and code preview dialogs.
3. Add unit tests in test/core/theme/querya_typography_test.dart validating font fallback definitions.