feat(cli): add an AI prompt for migrating to v4

[vladfrangu]

Adds crawlee upgrade-to-v4 so users can paste a migration prompt into an AI tool. The prompt guides project inspection, planning, migration and verification, with {SKILL_ROOT} replaced by the absolute path to bundled references.

Common breaking changes stay in the main prompt. Specialized APIs, Crawlee and Apify package roles, and Dockerfile and installation updates have separate references. Git guidance asks once for permission to create a migration branch and make incremental commits.

The CLI build bundles the prompt and references. The upgrade command uses the invoked CLI version even when the project has a local v3 installation.

Closes #4122.

Validation:

• Five CLI tests pass, covering prompt rendering, packaged references, special characters in paths, and delegation to a project-local CLI.
• CLI TypeScript compilation, command execution, and package dry run pass. All 13 skill assets are included in the published layout.
• Type-aware lint, formatting, skill validation and git diff --check pass.

[🤖] Codex using GPT-6.1-Sol