feat(gui): add logs panel with filtering options

[ralgar]

Summary

Adds a Logs panel in the GUI, with a follow toggle and filtering options.

Changes

• Add a ring buffer sink to the logger's internal state
• Ensure correct log level and flush behavior across all sinks
• Add a 'Logs' panel in the GUI with follow and filter controls
• Use raw log objects for filtering and formatting
• Colorize log levels using the previously established color palette

Testing

Manual testing with vkcube and all 3 input backends.

• VKSHADE_LOG_LEVEL is respected for file and stderr sinks
• The ring buffer sink always operates independently at trace level
• Follow and filtering controls behave correctly
• Text input in the filter box works on all three input backends

Acknowledgements

Thanks to @kakra for the exploratory work in #77.