Also email room subscribers on the first unread message, not just mentions (#67)

The previous pass only emailed on a mention. Corrected scope: the
room's first unread message triggers one debounced email (same shape
as #66), and every mention additionally emails regardless of that
debounce, since a mention shouldn't get silently absorbed by an
earlier plain message's already-sent notification.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

frontend/src/api/rooms.ts

@@ -68,9 +68,10 @@ export function hideDm(roomId: string): Promise<void> {
   return apiFetch<void>(`/api/rooms/${roomId}/hide`, { method: 'POST' })
 }
 
-// #67: per-viewer opt-in for email-on-mention in this room. 400s for a DM
-// (backend rejects it -- see set_room_email_notifications), so callers
-// should only expose the toggle for a non-DM room.
+// #67: per-viewer opt-in for email on this room's first unread message
+// and every mention. 400s for a DM (backend rejects it -- see
+// set_room_email_notifications), so callers should only expose the
+// toggle for a non-DM room.
 export function updateRoomNotifications(roomId: string, emailNotifications: boolean): Promise<void> {
   return apiFetch<void>(`/api/rooms/${roomId}/notifications`, {
     method: 'PATCH',

frontend/src/components/RoomInfoPanel.tsx

@@ -398,8 +398,8 @@ export function RoomInfoPanel({
         <div className="room-info-section">
           <div className="toggle-row">
             <div className="toggle-label">
-              <span className="t">Email me on mentions</span>
-              <span className="d">Sent only while you're offline</span>
+              <span className="t">Email notifications</span>
+              <span className="d">New messages and mentions, while you're offline</span>
             </div>
             <label className="switch">
               <input

frontend/src/types.ts

@@ -87,8 +87,9 @@ export interface MyRoomItem extends Room {
   // #52: the other participant, only for is_dm rooms -- see backend
   // schemas/room.py's MyRoomItem for why this is precomputed server-side.
   dm_partner: DmPartnerInfo | null
-  // #67: this viewer's own opt-in for "email me when mentioned here while
-  // offline" -- always false for a DM (see backend's message_events.py).
+  // #67: this viewer's own opt-in for email while offline -- the room's
+  // first unread message plus every mention (see backend's
+  // message_events.py). Always false for a DM.
   email_notifications: boolean
 }