[Tech Debt] Remove dead code: BuyCredits command

[sonikro]

Problem

The BuyCredits command is fully implemented in packages/entrypoints/src/commands/BuyCredits/ but is commented out in the command registry with a TODO:

// TODO: Uncomment when the Pricing Packages are ready
// buyCredit: {
//     name: "buy-credits",
//     definition: buyCreditsCommandDefinition,
//     handler: createBuyCreditsCommandHandlerFactory({...})
// }

Dead implemented code increases confusion — contributors may not know if this is intentional, broken, or in-progress.

Fix

1. Delete packages/entrypoints/src/commands/BuyCredits/ directory and all files inside
2. Remove the commented-out block and its import from commands/index.ts
3. When buy credits is actually ready to ship, it should be re-introduced in a new PR