Fix encoded IIIF image service IDs

[ewlarson]

Summary

• preserve the requested IIIF Image API service URL when the advertised @id differs only by percent-decoding
• continue honoring genuinely different canonical service IDs
• add a regression test for the University of Wisconsin encoded-slash identifier

Root cause

The Wisconsin info.json endpoint uses an encoded slash (%2F), but its @id returns the same identifier with a decoded slash. The viewer trusted the decoded @id, producing tile URLs that returned 404. The encoded tile URLs return 200.

Verification

• npm test -- --run src/__tests__/geoblacklight/leaflet_viewer_controller.test.js (13 passed)
• full frontend test suite (957 passed)
• production frontend build
• browser verification against 5WA3TYLSGTMK29A: four IIIF tiles loaded with encoded service URLs and nonzero image dimensions

Fixes #294