SingleFile CLI 2.15.2

Changes

• single-file-core is updated to 1.6.7, see https://github.com/gildas-lormeau/single-file-core/releases/tag/v1.6.7. For the CLI it means smaller archives, since an image served with identical bytes from two URLs is stored once and a stylesheet emptied by the unused-rules removal is no longer written as an empty file; a <style> element repeated verbatim in a page is now minified at the position of its last copy, so a conflicting rule between the copies no longer wins in the saved page; and the manifest.json of a frame records the frame's title
• The CI workflows run on Ubuntu 26.04

Co-authored by Claude (Claude Code)