[LittleLeaf1018]

Direct-to-main documentation correction, based on upstream main at 4ab9854dea3d84e38a59c25e0f5835a00cf8225f. The PR changes four documentation files and contains no commits from #284.

Changes

• Remove aggregate environment totals and per-backend counts from README, quickstart, introduction, and docs/CLAUDE.md.
• In the README, retain 89 only as a revision-bound count of top-level Hub case-data directories.
• Explain that this directory inventory does not establish distinct runtime-instantiable environments, solver availability, validation, or backend coverage.
• Document loader APIs by backend: MAIA maia.from_hf(...) and NEK NekEnv.from_hf(..., nproc=...); qualify download and offline-staging behavior by backend.

Source evidence

• Dataset revision cf5ef6748443ae72e9647f398487e98d421a7243 contains 89 top-level directories. The sorted directory-ID list SHA-256 is f05df1a337de060151b945a463ca9b5b7e6b3e5cc211433830f9518f1f661fb9.
• At HydroGym main commit 4ab9854dea3d84e38a59c25e0f5835a00cf8225f, HFDataManager.get_available_environments() calls list_repo_files() without a revision and returns unique first path components; it does not instantiate or execute those entries: source lines 354–371.
• The loader examples are checked against the pinned MAIA and NEK sources and their backend guides.

Validation

• git diff --check passes.
• Recounted the public Hub tree at the pinned revision with huggingface_hub 1.6.0; 1,471 nested file paths yield 89 top-level directory IDs.
• npm ci and npm run build pass in an isolated checkout. npm ci reports 60 audit findings in the existing lockfile; this change does not modify dependencies.
• GitHub reports no checks on the branch.

PR #284 remains a separate open draft that also touches these count claims. Maintainers should coordinate the overlapping documentation changes so the Hub directory inventory is not presented as runtime environment coverage.