patches: core-go-checksum — fix the actual sigv4 bug, not flexible-checksums

The previous version of the patch set RequestChecksumCalculation=WhenRequired,
which targeted the flexible-checksum middleware. That layer never causes the
seek; the bug is in the sigv4 dynamic-payload middleware, which only uses
UnsignedPayload over HTTPS. With s3-insecure=true to internal Garage the
SDK takes the ComputePayloadSHA256 branch and seeks the non-seekable body.

Updated patch:
- Swaps ComputePayloadHash middleware for v4.UnsignedPayload{} via
  opts.APIOptions in objects.NewClient — forces unsigned payload regardless
  of TLS.
- Adds s3.WithSigV4SigningRegion(region) to NewFromConfig so the V1 endpoint
  resolver can't override the signing region back to "default".

Mirrors phoebe-lab/srht/patches/core-go-checksum.patch (d8feacd).

init: superproject for SourceHut documentation mirror

29 upstream SourceHut repos pinned as submodules to their latest tags,
plus Claude tooling (skills, build-index script, INDEX inventory) and
phoebe-lab production patches that are not yet upstream.

Read CLAUDE.md and .claude/INDEX.md before exploring.