fix: resolve message command aliases in prefix command dispatch

[AboMeezO]

Summary

Fix prefix command aliases not being resolved when invoked through their alias.

For example, !testing worked, but !t silently failed when t was defined as an alias for testing.

Root Cause

prepareCommandRun passed usedCommandOverride to findCommandByRoute as allowFlatAliasFallback. Since normal message dispatch doesn't use a cmdName override, this was false, preventing alias resolution.

Fix

Removed the incorrect argument so findCommandByRoute uses its default alias fallback behavior.

Hierarchical routes remain unaffected.

Tests

Added coverage for:

• Prefix alias resolution
• Primary command name resolution
• Hierarchical routes
• Unknown commands

Files

• AppCommandHandler.ts
• AppCommandHandler.alias-resolution.test.ts