[FEATURE] Allow customizing or overriding Preview MCP's verification workflow

Preflight Checklist

• [x] I have searched existing requests and this feature hasn't been requested yet
• [x] This is a single feature request (not multiple features)

Problem Statement

The Preview MCP is amazing — it's enabled non-developers on my team to ship features using Claude Desktop. But it injects a hardcoded <verification_workflow> into the system prompt that can't be customized. I have a custom /test-app skill with project-specific testing steps (login with test accounts, check specific screens, test dark mode, etc.), but Claude ignores it and follows the injected default workflow instead — even when CLAUDE.md and skill descriptions explicitly say to use the skill. I've tried PostToolUse hooks and stronger wording but nothing reliably overrides the injected instructions.

Proposed Solution

Allow users to customize or disable the verification workflow while keeping the preview tools available. Options:

1. A config field (e.g., in .claude/launch.json or settings) to provide custom verification instructions that replace the default ones
2. A toggle to disable only the injected instructions without disabling the preview tools entirely (current toggle disables the whole MCP)
3. Have project-level skills/CLAUDE.md rules reliably take priority over MCP-injected instructions

Alternative Solutions

_No response_

Priority

High - Significant impact on productivity

Feature Category

Configuration and settings

Use Case Example

_No response_

Additional Context

_No response_