docs(agent): document model quick-picker in overflow menu

docs/web-ui/agent.md

@@ -63,18 +63,28 @@ through. Three flex columns:
     click opens the loose-ends flyout.
   - **Overflow button** (`⋯`): always visible. Opens a frosted popover
     (`#overflow-menu`, positioned outside the header to escape any
-    stacking context) with four rows: `↑ dashboard` (link), `↻ rebuild
-    container` (POST confirm, same action as the dashboard R3BU1LD
-    button), `↻ new claude session` (POST confirm → `POST
-    /api/new-session`; next turn drops `--continue`), `🔓 logout`
-    (POST confirm → `POST /api/logout`; SIGINTs any in-flight turn,
-    wipes OAuth credential files, flips the agent to `needs_login`
-    — session history preserved). All destructive actions require
-    one extra click to acknowledge — rare ops shouldn't live in the
-    primary state strip. The popover's display rules are scoped to
-    `:not([hidden])` so the `[hidden]` HTML attribute's UA `display:
-    none` isn't overridden by the author CSS's `display: flex` —
-    the popover stays hidden until JS removes the attribute.
+    stacking context) with four management rows followed by a model
+    quick-picker section: `↑ dashboard` (link), `↻ rebuild container`
+    (POST confirm, same action as the dashboard R3BU1LD button),
+    `↻ new claude session` (POST confirm → `POST /api/new-session`;
+    next turn drops `--continue`), `🔓 logout` (POST confirm → `POST
+    /api/logout`; SIGINTs any in-flight turn, wipes OAuth credential
+    files, flips the agent to `needs_login` — session history
+    preserved). All destructive actions require one extra click to
+    acknowledge — rare ops shouldn't live in the primary state strip.
+    Below a separator, a **model quick-picker** section labelled
+    `model` renders three one-click shortcuts: `haiku (fast)`,
+    `sonnet (balanced)`, `opus (powerful)`. Clicking a button POSTs
+    `/api/model` with the alias (same path as the `/model <name>`
+    slash command). The button for the currently-active model is
+    highlighted via the `active` class; `renderModelChip` keeps the
+    picker state in sync with live `model_changed` events so it stays
+    accurate when the model is changed from another session. Clicking
+    the already-active model closes the menu without an extra POST.
+    The popover's display rules are scoped to `:not([hidden])` so the
+    `[hidden]` HTML attribute's UA `display: none` isn't overridden by
+    the author CSS's `display: flex` — the popover stays hidden until
+    JS removes the attribute.
 
 `/api/state` is fetched once on cold load (+ while
 `status === 'needs_login_in_progress'`); all other updates arrive via