feat(health): add hybrid data verification mode

[drondeseries]

This PR introduces a hybrid data verification mode for the health checker.

Problem

The current health checker relies solely on STAT commands, which only verify if an article exists on the provider's index. Some providers report articles as existing even when the data is corrupted or missing (ghost files), leading to corrupted files being marked as 'Healthy'.

Solution

This PR adds a 'Hybrid Data Verification' option (default: disabled) that:

1. Downloads the first and last segments of the file.
2. Downloads a small random sample (up to 18) of other segments.
3. Uses STAT for the remaining segments.

This ensures that at least some actual data can be retrieved, catching 'ghost' files and header corruption without incurring the massive bandwidth cost of a full download verification.

Changes

• Added DataVerification to HealthConfig.
• Updated ValidateSegmentAvailabilityDetailed to support verifyData flag.
• Added UI toggle in Health Settings under 'Advanced Settings'.
• Implemented sampling logic for data verification.