GNU sort uses -h as --human-numeric-sort, with --help being long-only.
Free the -h slot so we can land --human-numeric-sort/-h next, matching
GNU semantics. --help (long form) still prints usage as before.

Co-Authored-By: Claude Opus 4.7 (1M context) <[email protected]>

Stale after dropping the -h alias for --help. Spotted by codex on #203.

Co-Authored-By: Claude Opus 4.7 (1M context) <[email protected]>

## Summary

- Implements GNU sort's `-h`/`--human-numeric-sort` ordering: by sign
(negative, zero, positive), then SI suffix magnitude (none < K/k < M < G
< T < P < E < Z < Y), then by numeric value within the same suffix.
- Multi-letter suffixes (\`Ki\`, \`Mi\`) are NOT recognised — only the
single byte directly following the digits is consumed, matching GNU
sort.
- Rejects \`-hn\` and \`-dh\` (GNU compat).

This is part of a stack enabling the host-remediation demo. The
canonical pipeline `du -sh /var/* | sort -rh` now matches the standard
incantation. Stacks on top of #203 (which freed the `-h` slot from
`--help`).

## Test plan

- [x] `make fmt` clean (\`gofmt -l .\` shows no output).
- [x] \`go test ./builtins/sort/... ./tests/...\` passes — including 9
new scenarios under
\`tests/scenarios/cmd/sort/flags/human_numeric_*.yaml\`:
- basic mixed suffixes (1.2G, 500M, 20K, plus no-suffix and equal-suffix
tie-break)
  - long-form flag \`--human-numeric-sort\`
  - reverse \`-rh\`
  - tie-break by numeric value within same suffix
  - no-suffix vs suffixed ordering
- negatives (sign category — neg < zero < pos; magnitude reversed within
negatives)
  - combined with \`-u\`
  - \`du -sh\`-style golden path with size + path columns
  - \`-hn\` rejection
- [x] New unit tests in \`builtins/sort/human_numeric_test.go\` covering
the parser (\`parseHumanParts\`) and the comparator (\`compareHuman\`)
for: SI suffix order, fractions, negatives, no-suffix, leading blanks,
leading-zero stripping, unparseable inputs, '+' as non-sign, and
lowercase non-\`k\` suffixes (not recognised).
- [x] All existing sort tests still pass.
- [ ] \`RSHELL_BASH_TEST=1 go test ./tests/ -run
TestShellScenariosAgainstBash -timeout 120s\`: blocked locally on a
Docker file-sharing issue (\`bash: /work/runner.sh: No such file or
directory\`) that is independent of this change. CI should still
validate.

## Notes

- Updated \`SHELL_FEATURES.md\` to advertise the new flag and SI suffix
list.
- Removed the now-stale
\`tests/scenarios/cmd/sort/help/short_help_flag.yaml\` scenario (it
asserted \`-h\` was rejected; that contract is replaced by the
human-numeric scenarios above).

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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Co-authored-by: Claude Opus 4.7 (1M context) <[email protected]>