Add configuration to set Marker Preview generation resolution

Feature request

Add configuration to set marker generation resolution.

Benefits

  • Preview markers at higher quality without loading the full video (usecase Stash TV - #14 by Dining9093)

  • Scalable for large collections; pre-generate lower-res or higher-res on demand

  • Flexible quality/performance tradeoff

Use cases

  • Users browsing via markers instead of watching entire videos

  • Users wanting precise preview quality

Current situation

Markers seem to be generated at a fixed 640x320 resolution with no option to adjust. Users who want higher quality previews must load the full video.

Proposed solution

Add a configuration option to select marker generation resolution (e.g., 320p, 480p, 720p, 1080p, or custom). Keep the current default for backward compatibility.