[workshop-sim] Repair: Add tool-routing decision card to step 6 (Install gh-aw)

[github-actions]

Problem

Step 6 is the highest-dropout step (40% of students who reach it). The root cause is that UI-preferred students, copilot-app users, and cloud-agent users arrive at a terminal-only install command with no clear guided path. A single [!IMPORTANT] callout exists but is easy to miss — especially for beginners who don't yet know what a Codespace is.

Simulation data: 6/15 students dropped at step 6; 0/17 UI-preferred students completed the workshop. Top pain points: "Extension install requires terminal — no UI alternative exists" and "Copilot app user has no terminal context."

Proposed Change

Replace the current single callout at the top of 06-install-gh-aw.md with a decision card — a short numbered list or table that appears before any commands:

> **Which environment are you using?**
> - 🖥️ **Terminal / VS Code / Codespace** → continue below
> - 🌐 **GitHub UI / Copilot web app** → [open a Codespace first](02a-setup-codespace.md), then return here
> - 🤖 **Copilot coding agent** → expand the section below for agent-specific install steps

Move the existing <details> block for cloud-agent users immediately after this card so it's visually connected to the routing decision.

Acceptance Criteria

• A decision card with 3 explicit routes (terminal, UI/web, coding-agent) appears at the top of step 6 before any install commands
• UI/web-app route links directly to 02a-setup-codespace.md with anchor to the Codespace creation step
• The cloud-agent <details> block is repositioned directly below the decision card
• npx markdownlint-cli2 "workshop/06-install-gh-aw.md" passes with no errors

Suggested Owner

copilot coding agent (content edit + lint validation)

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