M2: check for the skeleton reference table and apps-extra placement

Two possible gaps in Module 2 (PHP beginner, app anatomy), flagged when the older tutorial library was reviewed against the course on 2026-06-11. Both need confirming against the current content before doing any work — they may already be covered.

1. Skeleton file/folder reference table

Tutorial 2 in course/files/tutorials/ has a table covering every file in the app skeleton with its purpose. Good reference material at exactly the point a learner is staring at an unfamiliar directory tree.

2. Per-environment apps-extra placement

The source tutorial explains where to put the app for each environment — local Docker, Windows file explorer, Codespaces. content/shared/setup.md mentions the apps-extra/pinboard/ path, so check whether M2 needs it too or can simply reference the setup module.

Done when

Either both are present in M2, or it is recorded that they are covered elsewhere.

Review the current Module 2 content and compare it with course/files/tutorials/ for the skeleton file/folder reference table. Check content/shared/setup.md and the M2 material for the per-environment apps-extra placement, including local Docker, Windows file explorer, and Codespaces. Done means both topics are present in M2 or their coverage elsewhere is recorded.