Fix/better dashboard panels

[Lore09]

This pull request updates the default time span and granularity for attack trends in the dashboard, improves error handling in AI generation, and enhances the display of date ranges in charts. The most important changes are grouped below:

Dashboard Trends Defaults and Display:

• The default selected time span for attack trends is changed from 30 days to 7 days in both the UI (index.html) and the JavaScript logic (charts.js). The "7D" button is now active by default, and _trendsDays is set to 7. [1] [2]
• The backend now always uses hourly granularity for attack type trends, regardless of the selected time span, instead of switching to daily granularity for longer periods.
• The chart's period label logic is improved to correctly format and display date ranges, distinguishing between hourly and daily data for better clarity.

AI Generation Error Handling:

• The error handling in generate_html_for_path is refactored: on AI generation failure, the function now raises exceptions instead of returning an HTML error response, improving error propagation and logging.