feat(pgpm): add spinner to install command

[pyramation]

Summary

Adds animated spinner feedback to the pgpm install command for a better user experience. The spinner shows progress during:

1. Checking for missing modules (when called without arguments)
2. Installing modules (both explicit packages and auto-detected missing modules)

Uses the createSpinner function from inquirerer 4.2.0 (already available from the previous upgrade PR).

Review & Testing Checklist for Human

• Test spinner visually: Run pgpm install @pgpm/base32 in a real terminal and verify the spinner animates correctly
• Test auto-install flow: In a module with missing dependencies in .control, run pgpm install without arguments and verify both spinners appear (checking → installing)
• Verify non-TTY behavior: Run in a non-interactive environment (e.g., pipe output) to ensure spinner degrades gracefully

Recommended test plan:

cd /path/to/pgpm/module
pgpm install @pgpm/base32  # Should show spinner during install
pgpm install               # Should show spinner for checking + installing

Notes

• Requested by: Dan Lynch (@pyramation)
• Session: https://app.devin.ai/sessions/95ea22c05e164e99ac7770c57aed8b2d

[devin-ai-integration]

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