fix: preserve search shorthand with aliases

[NianJiuZst]

Summary

Fixes #136.

This restores the documented resource-level search shorthand:

mmx search "MiniMax AI latest news"

when a command group contains multiple child names that are aliases for the same command implementation.

Root Cause

The registry only auto-forwarded a resource group when it had exactly one child command. Adding search web as an alias for search query made the search group have two children, so mmx search <query> started resolving as an unknown command even though both children point to the same command.

Changes

• Keep the existing single-child auto-forward behavior.
• Add alias-only group forwarding when every child command points to the same command object.
• Add a regression test for mmx search "MiniMax AI latest news" style resolution.

Validation

• bun test test/commands/aliases.test.ts
• bun test
• bun run typecheck
• bun run dev search "MiniMax AI latest news" --dry-run --output json

[RyanLee-Dev]

Thanks for commit