Jay Moran's displays list and a display page answer on main, read-only #9466

First slice of #9208 (parked twice: the check went red on the palette roster test, a } else rule hit from main, and the review-budget timeout under load). Keep this pull to reading only.

Done looks like:

• [ ] src/web/pages/displays.ts, src/web/pages/display.ts and the read half of src/actions/displays.ts come from origin/incoming/jay-main (git checkout origin/incoming/jay-main -- <file>), adapting only wiring to main; his design kept.
• [ ] GET /:owner/:name/displays and GET /:owner/:name/displays/:display answer server-rendered with the securityFloor headers; an unknown display is a 404.
• [ ] A test seeds a repository with one display and asserts what the list and the display page show.
• [ ] Any palette entry added is also added to every expected roster in test/palette-roster.test.ts; bun scripts/gate.ts and bun scripts/design-lint.ts pass; new classes are named in docs/design/areas/displays.md.
• [ ] Commits carry Co-authored-by: Jay Moran.

Files: src/web/pages/displays.ts, src/web/pages/display.ts, src/actions/displays.ts, src/http/server.ts, docs/design/areas/displays.md, test/displays.test.ts, test/palette-roster.test.ts. Risks: no writes and no arcade host in this pull; if test/crew-review-budget.test.ts times out in a shard, say so in the pull rather than changing it.

Parked by the crew: the check stayed red through 2 automatic tries (pull #9477 closed). Planner: split this smaller, or rewrite what done looks like; a person can also say what to try.

Parked by the crew: the check stayed red through 2 automatic tries: healthz answers within 1 s throughout a boot beside a draining forge's batch of 8, and work starts once it lets go (pull #9495 closed).

Parked twice since a person last spoke here, so it is the planner's now. Every reason:

1. the check stayed red through 2 automatic tries (pull #9477 closed)
2. the check stayed red through 2 automatic tries: healthz answers within 1 s throughout a boot beside a draining forge's batch of 8, and work starts once it lets go (pull #9495 closed)

The planner splits it, replaces it with a fresh issue, or defers it; a person can also say what to try. Nothing starts here until then, and the board lists it.

Split into #9530 (the /displays list) and #9531 (the /:owner/:name/display page, read-only). This issue named routes Jay's branch does not have (/:owner/:name/displays/:display) and asked for both pages and their 900 lines at once; the second red was an unrelated boot test, which the new issues say to name in the pull rather than edit. #9467 and #9468 now wait for #9531.