style(frontend): Prettier config + one-time repo-wide format pass

Prettier 3 (pinned), printWidth 100, double quotes — chosen to match the existing
hand-formatting and minimise reflow. This commit is ONLY the mechanical format pass
(`prettier --write`) plus the config/ignore/scripts, isolated so it never pollutes a
feature diff. Verified behaviour-neutral: typecheck, eslint (0 errors), and vitest
all green before and after. See .git-blame-ignore-revs — `git blame` skips this sha.

frontend/src/components/ChatDock.tsx

@@ -2,7 +2,14 @@ import { useEffect } from "react";
 import { useTranslation } from "react-i18next";
 import { useQueryClient } from "@tanstack/react-query";
 import { ChevronDown, ChevronUp, X } from "lucide-react";
-import { closeChat, initDock, notifyIncoming, toggleMinimize, useDockChats, type DockChat } from "../lib/chatDock";
+import {
+  closeChat,
+  initDock,
+  notifyIncoming,
+  toggleMinimize,
+  useDockChats,
+  type DockChat,
+} from "../lib/chatDock";
 import { onMessage, onUnread } from "../lib/messagesSocket";
 import * as e2ee from "../lib/e2ee";
 import Avatar from "./Avatar";
@@ -37,7 +44,7 @@ export default function ChatDock({ meId }: { meId: number }) {
           notifyIncoming({ id: from.id, name: from.name, avatar_url: from.avatar_url });
         }
       }),
-    [qc, meId]
+    [qc, meId],
   );
 
   // Live badge sync: another tab/device read a thread → refresh this tab's unread count + list.
@@ -47,7 +54,7 @@ export default function ChatDock({ meId }: { meId: number }) {
         qc.invalidateQueries({ queryKey: ["message-unread"] });
         qc.invalidateQueries({ queryKey: ["conversations"] });
       }),
-    [qc]
+    [qc],
   );
 
   if (chats.length === 0) return null;
@@ -68,7 +75,10 @@ function ChatWindow({ chat, meId }: { chat: DockChat; meId: number }) {
     <div className="pointer-events-auto relative w-80 max-w-[calc(100vw-2rem)] glass rounded-2xl shadow-2xl flex flex-col overflow-hidden">
       {/* One-shot attention flash on a new message; keyed by the counter so it replays each time. */}
       {chat.flash > 0 && (
-        <div key={chat.flash} className="chat-flash pointer-events-none absolute inset-0 rounded-2xl z-base" />
+        <div
+          key={chat.flash}
+          className="chat-flash pointer-events-none absolute inset-0 rounded-2xl z-base"
+        />
       )}
       <div className="flex items-center gap-2 px-3 py-2 border-b border-border bg-card/50">
         <button
@@ -76,7 +86,11 @@ function ChatWindow({ chat, meId }: { chat: DockChat; meId: number }) {
           className="flex items-center gap-2 min-w-0 flex-1 text-left"
           title={chat.minimized ? t("messages.expand") : t("messages.minimize")}
         >
-          <Avatar src={chat.avatar} fallback={chat.name} className="w-7 h-7 rounded-full shrink-0 text-xs" />
+          <Avatar
+            src={chat.avatar}
+            fallback={chat.name}
+            className="w-7 h-7 rounded-full shrink-0 text-xs"
+          />
           <span className="font-semibold text-sm truncate">{chat.name}</span>
         </button>
         <button