chore: Bump intra-repo deps to v0.11.1

[mojatter]

Step 1 of the v0.11.1 release (see docs/releasing.md).

Bump the intra-repo require versions to v0.11.1 in the five modules that carry replace directives, so their published tags reference each other at the new version:

• s3, gcs, azblob, server: github.com/mojatter/s2 → v0.11.1
• s2env: s2, azblob, gcs, s3 → v0.11.1

cmd/s2-server is intentionally left at v0.11.0. It has no replace directives, so a GOWORK=off build (used by the e2e image and GoReleaser) resolves intra-repo deps from proxy.golang.org; it can only require v0.11.1 after those tags are published. It is bumped in a follow-up PR once the tags exist — same sequence as v0.11.0 (#119 → #120).

go.sum is unchanged: the replace directives resolve these modules locally, so no proxy hash is needed, and CI resolves them through go.work.

Verification

Local, with the CI toolchain (go1.25.10):

• go vet ./..., root + all submodule go test pass (workspace mode).
• GOWORK=off builds pass for cmd/s2-server (still on v0.11.0), server, and the s3 integ-test binary — i.e. the e2e build path is green.

Next steps

1. Merge this PR.
2. Tag the merge commit: v0.11.1 + the five submodule tags (push submodule tags batched, root tag alone).
3. Follow-up PR bumps cmd/s2-server to v0.11.1; tag cmd/s2-server/v0.11.1.
4. Replace the GoReleaser notes with a hand-written changelog.