Jay Moran's display model is on main: a display.json reads into items and selections, and the arcade shelf compiles and is tested #9329

Fresh copy of #9279. The reads it imports from src/core/repos.ts (listAdminOwnedRepos, readableRepoIds, repoDatesFor, listAllReposByOwner) landed on main at 5dc23ad25 in pull #9303, so nothing stands in front of this.

Replaces #9207.

Done looks like:

• [x] git checkout origin/incoming/jay-main -- src/display/config.ts src/display/items.ts src/display/known.ts src/display/selections.ts src/arcade/shelf.ts, adapting only imports to main.
• [x] Nothing imports src/display/launch.ts, src/arcade/host.ts or src/arcade/snapshot.ts yet.
• [x] test/display-model.test.ts reads a good display.json into items and selections, and refuses a malformed one with a named error.
• [x] bun x tsc --noEmit and bun test pass. Commits carry Co-authored-by: Jay Moran.

Files: the five above and the test. Risks: do not touch src/http/api.ts. If tsc names another missing import, add exactly that export from his branch and say so in the pull.

Planner: closing #9279 as split carried its dependency on #9273 over to this issue. #9273 had closed as dropped, and that dependency parked this one. I removed the edge: #9273's reads are on main at 5dc23ad25. #9208 now waits on this issue in place of #9279.

Reviewed pull #9338 at its head: ticked git checkout origin/incoming/jay-main -- src/display/config.ts src/display/items.ts src/display/known.ts src/display/selections.ts src/arcade/shelf.ts, adapting only imports to main.; Nothing imports src/display/launch.ts, src/arcade/host.ts or src/arcade/snapshot.ts yet.; test/display-model.test.ts reads a good display.json into items and selections, and refuses a malformed one with a named error.; bun x tsc --noEmit and bun test pass. Commits carry Co-authored-by: Jay Moran..