fix: remove conflicting index command registrations

[emecii]

What does this PR do?

Restore CLI startup after duplicate index-* subparser registrations were merged in 9b786b0. LeannCLI.create_parser() currently raises argparse.ArgumentError: conflicting subparser: index-browser before any command can run, including help and list.

Remove the seven duplicate registrations and shadowed handlers introduced from #269, retaining the implementation from #285, which explicitly superseded it. All 68 effective non-parser methods remain unchanged. Keep the established --max-count, --index-name, and recomputation behavior; update two documentation examples to match.

Related Issues

Follow-up to the integration of #269 and #285. This also removes the seven baseline F811 errors visible in #415, but contains none of its tokenizer changes.

Validation

• All 37 regression cases fail on current main with the duplicate-subparser error; the identical tests pass on the pre-merge parent and this fix.
• 76 focused/adjacent tests passed; two existing verbosity integration tests were excluded because they can read the real user registry.
• Repository-wide Ruff lint/format and all eight pre-commit hooks pass.
• Core wheel builds; isolated wheel import and command parsing pass.
• Synthetic fixtures exercise all seven command families, real argument parsing/dispatch, and shared-builder options without reading personal data or downloading models.

This restores startup and the previously accepted behavior. It does not resolve the pre-existing standalone-wheel reader packaging gap (apps.* is absent), implement stub readers, or change reader limits and platform support. Real personal-data ingestion, native vector builds, the full test suite, and cross-platform CI were not run locally.

Checklist

• Full uv run pytest; focused validation and exclusions are above.
• Code formatted and repository-wide Ruff checks pass.
• pre-commit run --all-files passes.

Implemented and tested with Codex assistance. No claim of personal human review is made.