Fix round 3 for Task 7 (N5, minor-to-important): fix round 2's
encodeURI(options.redirectTo) fixed the non-ASCII crash but broke the
most common real use of redirectTo -- a return-path query param that's
already percent-encoded (e.g. /login?next=%2Fdash) -- because encodeURI
also escapes "%", double-encoding it to %252Fdash. Replaced with
headerSafePath(), a codepoint loop that encodes only codepoints above
0x7f (matching isLocalPath's style: no regex, no source escapes) and
leaves "%" alone.
Added tests: an already-percent-encoded target round-trips unchanged;
a non-ASCII target still 303s without throwing and the location is
ASCII-only; a plain ASCII target passes through byte-identical.
Clintchiz
3f1fcd0d2d