docs: register s3 module in docs index config

[Oaklight]

Summary

The s3 module has been in manifest.json but was never added to
_scripts/module_index_config.yaml. As a result make docs-index emitted:

warning: module 's3' in manifest but not in config (excluded from docs index)

and s3 was silently missing from both the EN and ZH docs sites.

This adds s3 to the storage category and fills in its metadata
(description, replaces list, benchmark target). The boto3, minio reference
libraries match the existing bench-s3 extra in pyproject.toml.

Notes

• The regenerated docs/modules/index.md for both languages is already
  pushed to the docs_en / docs_zh worktree branches.
• s3.md doesn't exist as a doc page yet, so the index link is currently
  dead — same situation as profiler, which is also indexed without a page.
  Worth a follow-up to write both.

Test plan

• make docs-index runs clean with no warning
• s3 appears in the module table and the Storage section in both languages

[elena-oaklight]

Trivially correct — s3 was in the manifest but missing from the docs index config, so make docs-index warned and dropped it. This adds it to the right category with matching metadata.

What I checked

Area	Status
modules: [cache, persistdict, s3] placement under storage	✅ Correct category
Metadata fields (benchmark, replaces, desc_en/zh)	✅ Consistent with other entries; boto3, minio, s3fs matches bench-s3 extra in pyproject.toml
YAML syntax / indentation	✅ Clean
Insertion point (before depdetect)	✅ Alphabetical within category block
CI	⏳ Pending (YAML-only change, no code impact)

PR body correctly notes s3.md doesn't exist yet (same situation as profiler) — worth a follow-up to write both.

LGTM 👍

[clementine-oaklight]

Docs-only, single-file YAML change — straightforward.

Checked:

• s3 added to the storage category module list ✅
• Module metadata (descriptions, replaces, benchmark) filled in, both EN and ZH ✅
• benchmark: boto3 matches the bench-s3 extra in pyproject.toml ✅
• Placement in the modules map is consistent with the category grouping ✅

CI still pending but this is a config YAML change that won't affect lint or tests.

LGTM 👍