astro 5.1.6

#12956 3aff68a Thanks @kaytwo! - Removes encryption of empty props to allow server island cacheability
#12977 80067c0 Thanks @florian-lefebvre! - Fixes a case where accessing astro:env APIs or import.meta.env inside the content config file would not work
#12839 57be349 Thanks @mtwilliams-code! - Fix Astro.currentLocale returning the incorrect locale when using fallback rewrites in SSR mode
#12962 4b7a2ce Thanks @ascorbic! - Skips updating content layer files if content is unchanged
#12942 f00c2dd Thanks @liruifengv! - Improves the session error messages
#12966 d864e09 Thanks @ascorbic! - Ensures old content collection entry is deleted if a markdown frontmatter slug is changed in dev