fix(cli): space-form subcommands error instead of fake-succeeding; did-you-mean for flags

[DavidWells]

Split from #8300 (4 of 9). Stacked on #8329 — merge that first; GitHub will retarget this to main.

What

netlify sites delete my-precious-site used to print the sites help text and exit 0. Now:

 ›   Error: 'netlify sites delete' is not a command.
 ›   Did you mean 'netlify sites:delete my-precious-site'?
 ›   Run 'netlify sites --help' to see available subcommands.

(exit 2, stderr — flags/args are preserved in the suggestion, so netlify env list --json suggests netlify env:list --json)

Also: typo'd flags get did-you-mean suggestions, and unknown root-level flags name the commands that own them (netlify --jsno → '--json' is a flag of: env:list, status, ...).

Why it helps agents

This was the most dangerous false-success in the CLI: a script or agent doing cleanup reads exit 0 as "site deleted" when nothing happened. Exit 0 now always means the command actually ran, and the error names the exact corrected command so an agent self-corrects in one step.

Testing

• New unit tests covering both suggestion paths and the space-form guard
• typecheck ✓ lint ✓ 417 unit tests ✓ didyoumean/help snapshots unchanged

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