Remove deprecated top-level shopify webhook trigger alias

[alfonso-noriega]

WHY are these changes introduced?

The top-level shopify webhook trigger command was a hidden alias for shopify app webhook trigger. It rendered a "this alias will be removed in a future release" warning and forwarded the call. This PR removes the deprecated alias in preparation for the next major release.

Part of the deprecated-flag-removal stack: #7525 ← this PR → #7527.

WHAT is this pull request doing?

• Deletes packages/app/src/cli/commands/webhook/trigger.ts (the WebhookTriggerDeprecated class).
• The empty packages/app/src/cli/commands/webhook/ directory is also removed.
• Removes the import and the 'webhook:trigger' entry from packages/app/src/cli/index.ts.
• Regenerates packages/cli/oclif.manifest.json (the entry is removed from the manifest).
• The supported shopify app webhook trigger command (and its tests) are unchanged.

How to test your changes?

1. Run pnpm shopify webhook trigger --help and confirm it now fails with Command webhook:trigger not found.
2. Run pnpm shopify app webhook trigger --help and confirm the supported command still works.
3. Run pnpm shopify app webhook trigger ... end-to-end and confirm the webhook is delivered as before.

Checklist

• I've considered possible cross-platform impacts (Mac, Linux, Windows)
• I've considered possible documentation changes
• I've considered analytics changes to measure impact
• The change is user-facing — I've identified the correct bump type (patch for bug fixes · minor for new features · major for breaking changes) and added a changeset with pnpm changeset add

[github-actions]

⚠️ Potential Breaking Changes Detected

This PR contains changes that may break the existing contract.

@shopify/dev_experience — this PR contains breaking changes that require coordination for the next major release. This check will remain failed until a member of the team approves the workflow run.

💬 Head to #help-dev-platform to discuss timing and plan the release.

📦 Major Version Changesets

The following changesets request a major version bump:

Changeset	Package
remove-app-deploy-force-flag.md	'@shopify/app': major
remove-app-generate-extension-type-flag.md	'@shopify/app': major
remove-app-generate-schema-command.md	'@shopify/app': major
remove-app-release-force-flag.md	'@shopify/app': major
remove-app-scaffold-extension-command.md	'@shopify/app': major
remove-top-level-webhook-trigger-alias.md	'@shopify/app': major
remove-webhook-trigger-shared-secret-flag.md	'@shopify/app': major
thin-webs-notice.md	'@shopify/plugin-did-you-mean': major
thin-webs-notice.md	'@shopify/plugin-cloudflare': major
thin-webs-notice.md	'@shopify/create-app': major
thin-webs-notice.md	'@shopify/cli-kit': major
thin-webs-notice.md	'@shopify/store': major
thin-webs-notice.md	'@shopify/theme': major
thin-webs-notice.md	'@shopify/app': major
thin-webs-notice.md	'@shopify/cli': major
thin-webs-notice.md	'@shopify/e2e': major

🗑️ Removed Commands

The following commands were removed from the OCLIF manifest:

• webhook:trigger