fix: show full parent command path in subcommand usage errors

[shaanmajid]

Summary

• Subcommand runtime usage errors (e.g., npm stage approve without a <stage-id>) rendered the bare subcommand name (e.g., npm approve <stage-id>) and Run "npm help approve" for more info -- pointing at a command and help page that don't exist.
• The subcommand instance now carries its parent command name, so usage output and usageError render the full path (npm stage approve <stage-id>) and point to the real help page (npm help stage)

This fix applies to npm stage and npm trust.

Implementation

• lib/npm.js: set parentName on the subcommand instance during dispatch (and use the full joined path on the --help branch for parity).
• lib/base-cmd.js: the instance usage getter threads parentName into getUsage, and the help footer resolves to the top-level documented command.

References

Fixes #9403

[swarnim-dev]

Tested this locally and can confirm it works. Ran the test suite and everything passes:

• stage/approve tests: 5/5 ✅
• trust command tests: 71 assertions across 5 files ✅

The fix does what it's supposed to - error messages now show the full command path like "npm stage approve " instead of the broken "npm approve ". Verified it works for both stage and trust subcommands.

Code looks solid, no edge cases I can find, and there's good test coverage.

Ready to ship acc. to me!