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).

patches: ubuntu/genimg — move guest DNS override to end of script

patches: ubuntu/genimg — fix guest DNS (SLIRP proxy) and -p1 hint

patches: ubuntu/genimg — correct context lines for the network hunk

The previous version had stale context (EOF / fi / DHCP=yes) that didn't
match the actual recipe. Replace with the real surrounding lines (resolv.conf
nameservers above, Address=10.0.2.15/24 below) so `patch -p0` applies
cleanly on a fresh apk recipe tree.

patches: ubuntu/genimg — widen systemd-networkd match to Name=en*

Third hunk in the ubuntu/genimg patch. Upstream only writes
25-ens3.network matching Name=ens3, but on modern noble + virtio the
kernel names the interface enp0s3 instead, so DHCP never starts and
the build-worker times out in 'Waiting for guest to settle'. Rename
the file to 25-ethernet.network and broaden [Match] Name= to en*.

patches: track ubuntu/genimg nbd-settle and chroot-chown fixes

Two-bug patch against builds.sr.ht-images ubuntu/genimg, applied
out-of-band on work.lab.local but not yet upstreamed to sr.ht-dev.

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.