Extend check-env-docs to catch missing sidebar and catalog entries

[sergiopaniego]

Summary

check-env-docs only validates the per-env doc stubs. The docs sidebar (_toctree.yml) and the HTML catalog (environments.md) are maintained by hand, so forgetting them passes CI silently: qed_math has been missing its catalog card on main, and #1003 repeated the same pattern with latex_ocr. This PR extends sync_env_docs.py --check to fail when a stub is not listed in the sidebar or the catalog, and adds the missing QED Math card.

Type of Change

• Bug fix
• New feature
• Breaking change
• Documentation
• New environment
• Refactoring

Alignment Checklist

Before submitting, verify:

• I have read .claude/docs/PRINCIPLES.md and this PR aligns with our principles
• I have checked .claude/docs/INVARIANTS.md and no invariants are violated
• I have run /pre-submit-pr (or bash .claude/hooks/lint.sh and tests) and addressed all issues

RFC Status

• Not required (bug fix, docs, minor refactoring)
• RFC exists: #___
• RFC needed (will create before merge)

Test Plan

• python scripts/sync_env_docs.py --check passes on this branch (the new QED Math card closes the only existing gap).
• Negative test: removing any environments/<slug> link from environments.md (or its - local: entry from _toctree.yml) makes --check exit 1 with a message pointing at the missing entry and how to add it.
• --fix / --dry-run still only write stub files. They now print a manual reminder for missing sidebar/catalog entries, including stubs --fix just created, since the card content needs a human-written description.
• Orphaned stubs are excluded from the new checks: the fix there is deleting the stub, not listing it.
• ruff check clean on the script.

Claude Code Review

Reviewed inline: the new find_unlisted() is read-only, check semantics are unchanged for existing failure modes, and CI wiring (.github/workflows/test.yml) needs no changes since it already runs --check.

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Note

Low Risk
Documentation and CI validation only; no application runtime or security-sensitive code paths change.

Overview
sync_env_docs.py --check now fails CI when an environment doc stub exists but is missing from docs/source/_toctree.yml (sidebar) or docs/source/environments.md (HTML catalog). A new find_unlisted() step scans those files; orphaned stubs are skipped. --fix still only writes stub files but prints reminders to add sidebar/catalog entries manually, including slugs it just created.

environments.md gains a QED Math catalog card for qed_math, closing a gap that previously passed the old check.

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