refactor(cli): flatten keys export/import into dumpkeys/restore

[moonD4rk]

Flatten the keys export / keys import noun-group into flat verbs dumpkeys and restore, and drop the keys parent command, so the CLI is uniformly flat verbs: dump / dumpkeys / restore / list / version.

Pure rename — restore keeps the same flags and behavior as the old keys import. No functional change.

Part of the flat-verb CLI redesign for the cross-host decrypt workflow (#587), shipping in three PRs:

1. this PR — command surface (flat verbs).
2. cross-platform restore — decrypt browsers absent from the analyst OS (keys import fails for browsers not available on the analyst OS #606).
3. zip transport — archive + restore --data-zip (Add a command to archive a browser's data files into a zip for cross-host keys import #607).

Refs #587.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 73.63%. Comparing base (8bd7c4e) to head (b0d2b26).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #608   +/-   ##
=======================================
  Coverage   73.63%   73.63%           
=======================================
  Files          67       67           
  Lines        2989     2989           
=======================================
  Hits         2201     2201           
  Misses        591      591           
  Partials      197      197           

Flag	Coverage Δ
unittests	73.63% <ø> (ø)

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[Copilot]

Pull request overview

This PR continues the CLI redesign by flattening the former keys export / keys import noun-group into top-level verb commands (dumpkeys and restore), removing the keys parent command to keep the CLI consistently verb-oriented.

Changes:

• Remove the keys parent command and rename keys import to the top-level restore command.
• Introduce a new top-level dumpkeys command (formerly keys export).
• Register the new commands in the root command setup.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated no comments.

File	Description
cmd/hack-browser-data/restore.go	Removes the keys command group and defines restore as the new top-level replacement for keys import.
cmd/hack-browser-data/main.go	Updates root command registration to add dumpkeys and restore and drop keys.
cmd/hack-browser-data/dumpkeys.go	Adds the new dumpkeys top-level command (extracted from the prior keys export implementation).

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