docs(web-ui): matrix-accounts picker reads state.containers

The M4TR1X ACC0UNTS section said the agent picker is populated from
`state.agents`, which never existed on /api/state — the same stale
field the code read. Sync the doc to the live roster field.

docs/web-ui/dashboard.md

@@ -214,7 +214,7 @@ title). Its own esbuild bundle (`matrix-accounts.js`); no SSE — it reads
 `/api/state` once for the agent picker and otherwise works off two
 purpose-built endpoints.
 
-An agent picker (populated from `state.agents`) drives a list of that
+An agent picker (populated from `state.containers`, the live roster) drives a list of that
 agent's configured accounts — name, homeserver, and a token-status dot —
 read from `GET /api/matrix-accounts?agent=<name>` →
 `{ accounts: [ { name, homeserver, token_present } ] }`. The status

frontend/packages/dashboard/src/matrix-accounts.js

@@ -31,7 +31,10 @@ async function loadState() {
     if (!resp.ok) return;
     const s = await resp.json();
     renderServerWarnings(s.server_warnings);
-    agents = (s.agents || [])
+    // `/api/state` exposes the live roster under `containers` (each entry an
+    // object carrying `.name`); there is no top-level `agents` field, so the
+    // picker stays compatible with both string + object shapes defensively.
+    agents = (s.containers || [])
       .map((a) => (typeof a === 'string' ? a : a && a.name))
       .filter(Boolean)
       .sort();