Update app-builder-skill

[tkallady]

Summary

Reworks forge-app-builder into a progressive-disclosure skill that also supports changes to existing apps.

The rewrite uses an intent-based routing based setup to load task-specific instructions and route debugging, security, release-readiness, cost, and connector work to the appropriate specialist skills.

What changed

• Replaced the monolithic workflow with intent-based routing and conditional capability guides.
• Added focused references for:
  • New and existing apps
  • Module selection
  • UI Kit and Custom UI
  • Backend functions and events
  • APIs, permissions, scopes, and egress
  • Storage and data residency
  • Environments and configuration
  • Distribution and access
  • Validation and release
• Added safety boundaries around credentials, terms acceptance, billing consent, deployment, installation, upgrades, and production changes.
• Added Forge MCP configuration for Codex
• Expanded eval coverage for planning, scaffolding, extending existing apps, Preview features, permissions, storage, secrets, releases, and specialist routing.
• Added an existing UI Kit fixture for extension scenarios.
• Retained the existing tested scaffolding, template, environment, and deployment helper scripts.
• Made only minor freshness updates to those scripts:
  • Removed hard-coded Node.js version wording.
  • Removed stale template-count and verification-date claims.
• Updated the frontmatter to move additional non-spec metadata into a metadata field.

Validation

New skill was tested using agent benchmarking tool, and was found to score similarly to the previous skill with Cursor CLI.