feat!: own the module path and drop the Silo Go SDK replacement

[Vonng]

Declares module github.com/pgsty/silo-pkg/v3 instead of continuing to claim upstream's github.com/minio/pkg/v3, and drops the pgsty/silo-go replacement in favour of upstream minio-go.

Why the path change

Keeping upstream's path made this fork selectable only through a replace directive, and Go does not inherit those from dependency modules. Three concrete costs showed up while preparing the next Silo release:

• every consumer had to repeat the redirect, and one that forgot built against upstream silently;
• the require line had to name an upstream version this source no longer matches — ParseConfigStrict first appears upstream in v3.11.0 and Resource.IsBareARN exists in no upstream version at all;
• pgsty/mc needed a compile-time sentinel to turn that silent downgrade into a build failure, and raising its floor to make the metadata honest propagated through the graph and forced silo-console's deliberately low floor upward.

The upstream path has little to offer in return here: minio/pkg is a 33-star internal library, and this module's consumers are silo, silo-console, and mc. The Silo Go SDK keeps upstream's github.com/minio/minio-go/v7 path, where drop-in compatibility is worth having.

Why drop the Silo Go SDK replacement

pgsty/silo-go carries no functional divergence from upstream. Its only unique change, Return CopyObject checksums in UploadInfo, was merged upstream on 2026-08-24; everything else in the fork is a version string, a logo, a README, and a lint-tool block.

Upstream's newest tag v7.3.0 predates that merge by 14 commits, including #2290 fix: race on shared checksum hasher in parallel multipart upload, so pinning the tag would be a regression. This requires v7.3.1-0.20260828014306-0e78d3f18efe until upstream tags again.

Consumer impact

Consumers still on the old arrangement keep building against the versions they already pinned. To move: drop the replace, require this path, rewrite the imports.

Verification

• go build ./..., go vet ./..., go mod tidy -diff, gofmt -l . clean
• go test ./... — 23 packages pass
• The downstream migration was validated end to end against this branch before it was opened: mc (194 files), silo-console (36 files), and silo (181 files) all build, vet, and pass their suites; silo's rebrand guard passes with a compatibility-baseline diff of exactly 19 deleted import entries and no change to env, metrics, headers, routes, policy values, or exported symbols.