Clarify non-leaf hierarchical command handlers

[AboMeezO]

Summary

This PR clarifies and improves non-leaf hierarchical command handling.

A parent hierarchical command file can still define metadata/config, but executable handlers must live on leaf nodes.

src/app/commands/
└── [admin]/
    ├── command.ts        # non-leaf node: metadata/config is valid here
    └── [logs]/
        └── command.ts    # leaf node: executable handlers belong here

If [admin]/command.ts exports chatInput, message, or autocomplete while [admin] has children, CommandKit now logs a highlighted warning, ignores those executable exports, and continues loading valid leaf routes like /admin logs.

The router diagnostic remains as secondary scan feedback, but the main developer-facing fix now happens in the runtime loader.

Tests

• .\node_modules\.bin\vitest.CMD run src/app/handlers/AppCommandHandler.hierarchical.test.ts src/app/router/CommandsRouter.test.ts
• pnpm --dir packages/commandkit build
• pnpm --filter test-bot build
• pnpm --filter test-bot start with PORT=54346; verified the warning appears and command loading continues, then local startup stops at invalid Discord token

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