fix(date): `date -r` does not return file modification time

[chaliy]

Summary

date -r <file> should return the file's modification time, but in bashkit it returns an empty/current timestamp instead.

Reproduction

touch /tmp/test.txt
date -r /tmp/test.txt +"%B %d, %Y"
# Expected: file's modification date
# Actual: empty or current time

Context

Discovered while running bashblog via bashkit CLI. Bashblog uses date -r extensively to:

• Read post timestamps: LC_ALL=C date -r "$i" +"$date_format_full"
• Generate archive headers: date -r "$i" +"$date_allposts_header"
• Format dates for RSS feed: date -r "$i" +"$date_format_full"

Without this, all timestamps in the generated blog are empty.

Expected behavior

date -r <file> +<format> should stat the file on the VFS and format its modification time.