forge.json's app.looks names the five pages the owner opens most, and a test proves each answers 200 #2801

A smaller first step than #2783. The list starts short and true.

Done:

• [ ] forge.json app.looks is / /board /map /apps /settings
• [ ] new test/forge-looks.test.ts: forge.json parses, and each path in app.looks answers 200 (not a redirect) to an admin on a fresh forge
• [ ] the pull's preview deploys, and its looks show the five pages

Files: forge.json, test/forge-looks.test.ts.

Replaced by #2809. A builder left this one with no pull. #2809 is smaller: three pages instead of five, read through the manifest parser, with the exact helper to sign in an admin.