Add prominent migration notice to all pages indicating Jacdac has moved to https://github.com/jacdac

[Copilot]

This PR adds a prominent migration alert to every page of the Jacdac documentation website to inform users that the project has moved to the new GitHub organization at https://github.com/jacdac.

Changes Made

• Created MigrationAlert.tsx component: A new alert component that displays a warning-level notification with an attention-grabbing emoji and clear messaging about the migration
• Integrated into main layout: Added the alert to layout.tsx so it appears consistently at the top of every page across the entire website
• Follows existing patterns: Uses the same Material-UI Alert component and lazy loading pattern as other site-wide alerts like FirmwareAlert and PassiveAlert

Implementation Details

The migration alert:

• Uses severity="warning" to ensure it's visually prominent
• Includes a direct link to the new GitHub organization
• Appears before other page content to maximize visibility
• Is styled consistently with the existing design system
• Opens the new location in a new tab with proper security attributes

Visual Impact

The alert will appear as a yellow warning banner at the top of every page with the message:

📢 Important: Jacdac has moved!
The Jacdac project has moved to https://github.com/jacdac. Please update your bookmarks and references to point to the new location.

This ensures all users visiting any page of the documentation are immediately informed about the migration and can easily navigate to the new location.

Warning

Firewall rules blocked me from connecting to one or more addresses

I tried to connect to the following addresses, but was blocked by firewall rules:

• analytics.gatsbyjs.com
  • Triggering command: /usr/local/bin/node /home/REDACTED/work/jacdac-docs/jacdac-docs/node_modules/gatsby-telemetry/lib/send.js (dns block)
  • Triggering command: /usr/local/bin/node node_modules/gatsby/cli.js develop (dns block)
  • Triggering command: /usr/local/bin/node node_modules/gatsby/cli.js build (dns block)
• https://storage.googleapis.com/chromium-browser-snapshots/Linux_x64/1095492/chrome-linux.zip
  • Triggering command: /usr/local/bin/node install.js (http block)
• unpkg.com

If you need me to access, download, or install something from one of these locations, you can either:

• Configure Actions setup steps to set up my environment, which run before the firewall is enabled
• Add the appropriate URLs or hosts to the custom allowlist in this repository's Copilot coding agent settings (admins only)

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[pelikhan]

Nope can't merge.

[thomasjball]

@pelikhan - Please make sure that https://microsoft.github.io/jacdac-docs/tools/makecode-sim/ does not get banner.