forge.json's app.looks names /, /board and /map, and a test proves each answers 200 to an admin #2809

Replaces #2801, which a builder left with no pull. Smaller: three pages, one test file.

Done:

• [ ] forge.json has "looks": ["/", "/board", "/map"] under app, and src/apps/manifest.ts accepts it
• [ ] new test/forge-looks.test.ts: read forge.json through the manifest parser in src/apps/manifest.ts, start a forge, sign in an admin with test/helpers/admin.ts adminCookie, and expect each listed path to answer 200 (redirect: manual)

Files: forge.json, test/forge-looks.test.ts. Run that test and the manifest tests before pushing.

Done on main already, waiting for you to close it: 74363e0cdd62f837c08f9c9180945ae64f376b6d

Closed: already done on main in 74363e0.