Promotes a possibly-relative Tiltify URL into an absolute URL.
"/@user/campaign"
"https://tiltify.com/@user/campaign"
"https://tiltify.com/+team/x"
"//cdn.tiltify.com/x"
""
null
undefined
Idempotent: calling twice on an already-absolute URL is a no-op.
Promotes a possibly-relative Tiltify URL into an absolute URL.
"/@user/campaign"→"https://tiltify.com/@user/campaign""https://tiltify.com/+team/x"→ unchanged"//cdn.tiltify.com/x"(protocol-relative) → unchanged""/null/undefined→""Idempotent: calling twice on an already-absolute URL is a no-op.