fix(sync): literal regex replacements and script-safe embedded JSON

replace_between now passes a callable to re.sub so backslashes in
generated content stay literal instead of crashing or expanding group
references. Registry and search-index JSON embedded in script tags
escapes <, > and & as unicode escapes so content can never close the
block. Writes use LF line endings.

Closes #106

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Signed-off-by: TMHSDigital <154358121+TMHSDigital@users.noreply.github.com>

Author: TMHSDigital