Fix image parsing in middleware

[sjmiller609]

Note

Fixes image name handling by decoding URL-encoded path params in ResolveResource (uses url.PathUnescape before calling resolvers). This ensures names like docker.io/library/nginx:alpine work when passed as %2F/%3A encoded segments.

• Update lib/middleware/resolve.go to decode {name} for /images/{name} prior to resolution
• Add lib/middleware/resolve_test.go to verify resolver receives decoded names across multiple cases
• Extend cmd/api/main_test.go with end-to-end tests (via oapi.HandlerFromMux) asserting handlers get decoded image names and avoid 400s

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