agents: drop the count and the coverage claim (FRE-359 verdict B)

FRE-359's verdict is B: the page's thirteen is the registry's first thirteen
of eighteen rows, so the count, "every coding agent The Nook supports" and
"Supported agents" all overstate or understate the app. The permitted
sentences are the CTO's, verbatim.

- agents.tsx: head description, ogTitle and H1 paragraph replaced with the
  verdict's sentences; title/H1 "Supported agents" -> "Agent coverage".
- agents.test.ts: the stale NOOK-336 guard asserted "all thirteen" and
  the 13-name roster, so it passed in lockstep with the page. It now asserts
  no count of any form, no completeness phrase, and that the rows are a
  subset of the 18-name registry list (copied 2026-10-29, @ f4258034) in
  registry order. The table still lists 13 rows; regenerating it from the
  registry is its own ticket, and the guard no longer pretends otherwise.
- FeatureBreakdowns.tsx / IslandExtras.tsx: the landing "13 agents:" bullet
  and the "13 agents" marquee chip lose the count; the chip becomes
  "Agents wired in".

bun test src/routes/nook/agents.test.ts: 4 pass. Server security and appcast
suites fail in this checkout on missing env (Environment validation failed /
mainDBConnection), unrelated to these files.

Co-Authored-By: Paperclip <noreply@paperclip.ing>

src/components/nook/IslandExtras.tsx

@@ -722,7 +722,7 @@ function LayoutMock() {
 /* ── Marquee ─────────────────────────────────────────────────────── */
 
 const CHIPS_A = [
-  "13 agents",
+  "Agents wired in",
   "Custom agents",
   "Six chiptunes",
   "Focus-aware slots",