feat: add ruborg validate repo --repair for passphrase-injected borg check --repair

[mpantel]

Summary

• Adds Repository#repair that runs borg check --repair with YES\n piped to stdin via Open3.capture3, capturing output for logging.
• Adds --repair and --yes options to ruborg validate repo; --repair without --yes raises a ConfigError to prevent accidental data loss.
• Repair output (affected segments/archives) is printed to stdout and written to the ruborg log file.
• Rubocop: no new offenses introduced.

Closes #17

Test plan

• bundle exec rspec spec/ruborg/repository_spec.rb -e "repair" — 4 examples pending (Borg not installed in CI), 0 failures.
• bundle exec rspec spec/ruborg/cli_spec.rb -e "validate repo --repair" — 3 examples pending, 0 failures.
• bundle exec rubocop lib/ruborg/cli.rb lib/ruborg/repository.rb — same offense count as baseline (all pre-existing).
• Manual: ruborg validate repo -r myrepo --repair → raises error asking for --yes.
• Manual: ruborg validate repo -r myrepo --repair --yes → fetches passphrase from Passbolt, runs borg check --repair, logs output.

🤖 Generated with Claude Code

[mpantel]

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