fix: URL-decode DID path params for percent-encoded colons
ureq 3.x encodes colons in URL paths as %3A, but chi's URLParam
returns the raw (encoded) value. This caused 500 errors when
pijul-pad tried to pull from knot with encoded DID paths.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>