fix(web): paint session row highlight as one chip including the menu

Selected and hover fill stay on the whole row. The title and ⋯ no longer draw their own canvas or radius, so they stop looking like two controls (BUG-993, recurrence of BUG-024).

frontend/DESIGN.md

@@ -357,7 +357,7 @@ The birth-time rectification session is the consultation transcript plus a house
 - **States:** default, hover, current, focus, disabled.
 - **Hierarchy:** section labels stay tertiary; session titles and primary actions use ink so history rows do not collapse into the same gray as “收藏对话 / 历史对话”. History groups use the overline token for “今天 / 昨天 / 最近 7 天 / 最近 30 天 / 更早”. When the chart is not the account holder, a secondary line shows the chart name under the title. A session title is named when it is created; opening a stored session must not rename it. `updatedAt` advances only on conversation activity, including rectification turns, choice, adopt, and stop. Opening, refresh, and metadata PATCH do not bump it. A `?c=` that is not on the loaded page is looked up with `GET /api/sessions/{id}` before anyone may say it was deleted. Locked by `frontend/tests/session-open-preserves-identity.test.ts` and `frontend/tests/session-lookup-unlisted.test.ts`.
 - **Request behavior:** existing sessions remain selectable for reading while a request is active; creating or sending another request stays locked until the active request settles.
-- **Surface:** translucent warm-gray sidebar; current uses a white glass surface and deep-brown marker.
+- **Surface:** translucent warm-gray sidebar. Current and hover fill the whole `.session-row` — title and the ⋯ share one chip. The menu trigger has no canvas of its own.
 
 ### Sidebar shell