Improve AT Protocol URI workaround for all DID methods

Replaced the narrow did:plc-only fix with a comprehensive solution that
handles all AT Protocol URIs by percent-encoding the authority component.
Now supports did:web, did:key, and other DID methods, plus handles edge
cases like URIs without path components.

The fix detects at:// URIs, extracts the authority part, percent-encodes
it if needed, and reconstructs a valid URL that JavaScript can parse.

Addresses feedback in #436

Co-Authored-By: Claude <noreply@anthropic.com>