Function to_canonical_uri 

pub fn to_canonical_uri(loc: &S3Location) -> String

Encode an S3Location into its canonical brows3r:// URI.

The canonical form uses the stable profile_id (not the display name) so two profiles with identical display names produce different URIs (AC-2).

Key path separators (/) are preserved for readability; all other non-alphanumeric characters (including ?, #, %, unicode) are percent-encoded.