[Bug]: Built-in debug-keys command is unreachable due to legacy-like classifier

[ben-ranford]

Bug Description

The built-in first-class command debug-keys is unreachable because the legacy-like syntax classifier rejects any hyphenated top-level token before command routing.

Steps to Reproduce

1. Run ggc debug-keys
2. Observe output:
   • Error: legacy-like syntax is not supported.
   • Use unified subcommands. See: ggc help <command>

Expected Behavior

debug-keys should execute normally (or show its command help), because it is a registered first-class command.

Screenshots

N/A

Environment

• OS: Darwin 25.2.0
• Go Version: go1.25.7 darwin/arm64
• ggc Version: v1.0.0
• git Version (run git --version): 2.39.5 (Apple Git-154)

Additional Context

debug-keys is registered in the command registry, but isLegacyLike() currently classifies any hyphenated top-level command as legacy syntax and exits before router dispatch.

Relevant locations:

• cmd/cmd.go (legacy-like detection)
• cmd/command/registry.go (debug-keys registration)

closes #339