Step 21b/23 (Phase 6): Docs — Update CLI_USER_DOC with all commands, flags, and exit codes

[Jordan231111]

Summary

Update `docs/CLI_USER_DOC.md` to be the definitive CLI reference, covering every command, subcommand, flag, and exit code.

Depends On: All CLI commands implemented
Parent Issue: #15 (Documentation Completion)
Related: #89 (Fix documentation to include all commands)

Key Changes

1. Document every command with:
   • Synopsis (command + flags)
   • Description
   • Options/flags table
   • Example usage
   • Expected output
2. Commands to document:
   • `scan` (--deep, --threads)
   • `hash` (file path)
   • `update-db` (--force)
   • `schedule-updates` (--hours)
   • `quarantine-file` (path)
   • `list-quarantined`
   • `restore` (id, --force)
   • `remove` (id, --force)
   • `remove-file` (path, --force)
   • `scan-url` (url)
3. Exit codes section: 0, 1, 2 with descriptions
4. Troubleshooting section: common issues and fixes
5. Environment variables if any are supported

Acceptance Criteria

• Every command and subcommand is documented
• All flags and options are listed with descriptions
• Examples are provided for each command
• Exit codes are documented
• Troubleshooting section covers common issues
• Document matches actual binary behavior (tested)