refactor: use @heroku/sdk for apps:rename and apps:stacks:set commands

[tlowrimore-heroku]

Summary

• Migrate src/commands/apps/rename.ts from raw this.heroku.patch to platform.app.update via @heroku/sdk.
• Migrate src/commands/apps/stacks/set.ts from raw this.heroku.patch to platform.app.update via @heroku/sdk.
• Drop the deprecated @heroku-cli/schema imports in both files; SDK method return types are inferred from @heroku/types/3.sdk.
• Rewrite both unit test files to stub HerokuSDK.prototype.platform, dropping nock. Test counts and observable output unchanged.

Type of Change

Breaking Changes (major semver update)

• Add a ! after your change type to denote a change that breaks current behavior

Feature Additions (minor semver update)

• feat: Introduces a new feature to the codebase

Patch Updates (patch semver update)

• fix: Bug fix
• deps: Dependency upgrade
• revert: Revert a previous commit
• chore: Change that does not affect production code
• refactor: Refactoring existing code without changing behavior
• test: Add/update/remove tests

Testing

• tsc clean vs. baseline (scripts/codemods/sdk-migration/tsc-delta.sh empty)
• eslint clean on changed files
• mocha for test/unit/commands/apps/rename.unit.test.ts passes (2/2)
• mocha for test/unit/commands/apps/stacks/set.unit.test.ts passes (3/3)
• mocha for sibling test/unit/commands/apps/**/*.unit.test.ts passes (89/89)
• Manual smoke against a real app: heroku apps:rename --app <old> <new> (verify URL output and git-remote rewrite)
• Manual smoke against a real app: heroku apps:stacks:set heroku-24 -a <app> (verify pending vs. immediate-update message paths)

Related Issues

GUS work item: W-22264732

[michaelmalave]

LGTM!