QR scan entry point for OID4VP Authorization Requests

### Description
Extend the existing `/scan` page to also detect and route OID4VP Authorization Request QR codes. A presentation request URI typically looks like:

### Acceptance criteria
- [ ] The scanner distinguishes between an issuance offer URI and a presentation request URI
- [ ] On detecting an OID4VP request, the user is routed to `/presentation/request`
- [ ] Unrecognised or malformed URIs show a clear error state
- [ ] The parsed request object (or `request_uri`) is stored in a state provider, accessible downstream
- [ ] Unit tests cover the URI-type detection logic

Start at the existing `/scan` page and trace how scanned URIs are currently classified and routed. Add unit tests for distinguishing issuance offers, OID4VP requests, and malformed or unrecognised URIs; done means valid requests reach `/presentation/request`, the parsed request or `request_uri` is available from the state provider, and invalid input shows a clear error state.

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