Split Quick Start into included-example and external-project tutorials

[alonshoa]

Problem

The current Quick Start is useful for validating this repository, but it does not separate "try the included examples" from "create or run your own external project." That makes the first-run experience ambiguous for external users.

Scope

• Split the current Quick Start into a repo-example tutorial and an external-project tutorial.
• Keep the included-example path focused on rendering a known registered scene and inspecting its build.
• Keep the external-project path focused on the smallest currently supported manual setup.
• Add expected output blocks after important commands: list, validate, render, inspect.
• Cross-link concepts only after the tutorial steps introduce the relevant terms.

Acceptance Criteria

• A user can complete the included-example tutorial from a clean checkout using the supported runtime path.
• A user can follow the external-project tutorial without reverse-engineering repository internals.
• The tutorials clearly identify when commands run on the host versus inside Docker/devcontainer.
• mkdocs build --strict passes.

Dependencies

Depends on the command verification from the docs gap audit. Must not claim that studio init or a Windows installer exists.

Category

documentation, onboarding, external-projects