SingleFile CLI 2.21.0

CLI fixes and improvements

Updated single-file-core to 1.8.0
- Filename templates: the page text variables ({page-title}, {page-heading}, {page-description}, {page-author}, {page-creator}, {page-publisher}) decode HTML character references a second time, so a site that escapes its title twice no longer leaves & in the filename (#2036 by @TheGhost78)
- Filename templates: [Nch] now keeps N characters, counted by code point, instead of N bytes (#2037 by @TheGhost78)
- The proof of existence hash is computed on the final bytes of a compressed page (#2028 by @johanjohan)

Co-authored by Claude (Claude Code)