fix(swagger): match go-openapi/loads' DocLoader signature at v0.25+

[hsinatfootprintai]

Closes #146.

What broke, and why it's not obvious from this repo alone

go-openapi/loads v0.25.0 added a variadic loading.Option parameter to the exported DocLoader type. RenderDoc()'s embedFsLoader closure kept the pre-v0.25 signature, so it stops satisfying loads.DocLoader the moment anything in a build's dependency graph pulls loads past v0.22.x — direct or transitive. This repo still pins loads at v0.22.0, so it builds clean today; the break only shows up in a consumer's build once their own dependency graph (this repo included as a dependency) resolves a newer loads. grandturks hit it through a routine go-openapi/validate dependabot bump, with no way to work around it from their side — Go doesn't let a downstream module patch a dependency's function signature.

What changed

• pkg/swagger/collections/apidoc.go: embedFsLoader now accepts the variadic loading.Option param (unused — the embedded FS loader needs none of what loads.Spec's callers can pass through it, e.g. a custom HTTP client or timeouts)
• go.mod/go.sum: bumped go-openapi/validate to v0.26.4 (pulling loads to v0.25.1) so the fix is actually exercised by this repo's own build, rather than left latent for whoever bumps it downstream next

Test evidence

• Reproduced first: bumped go-openapi/validate/loads locally and confirmed the exact compile error from grandturks's dependabot PR
• go build ./..., go vet ./... clean
• go test ./... -short — all green, including TestCollectionDoc (pkg/swagger/collections), which exercises RenderDoc() directly and produces the identical rendered document before and after — this is a signature adaptation, not a behavior change
• vendor/ is gitignored and regenerated in CI (go mod tidy && go mod vendor), so nothing to commit there

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