litebastion: More liberal than the spec, it accepts uppercase key hashes in URLs

Spec says that in `https:////`, the key hash MUST be lower-case hex. While litebastion accepts any mix of upper and lowercase. One could consider this a spec issue, but it makes sense for the implementation to be as strict as the spec says.

Start by locating litebastion's URL parsing and the code that validates the key hash in the documented URL structure. Confirm how mixed-case hexadecimal hashes are currently handled, then verify that uppercase hashes are rejected and lower-case hashes remain accepted.

Written by the indexing model from the issue text.