feat: per-user assistant name and system prompt customization

Each user can rename the AI assistant and edit their own system prompt in Settings.

src/modules/agent/components/assistant-panel.tsx

@@ -15,9 +15,10 @@ import {
 type Props = {
   configured: boolean;
   userId: string;
+  assistantName: string;
 };
 
-export function AssistantPanel({ configured, userId }: Props) {
+export function AssistantPanel({ configured, userId, assistantName }: Props) {
   const [messages, setMessages] = useState<AssistantChatMessage[]>(() => loadAssistantChat(userId));
   const [input, setInput] = useState("");
   const [error, setError] = useState<string | null>(null);
@@ -144,7 +145,7 @@ export function AssistantPanel({ configured, userId }: Props) {
                 style={message.role === "assistant" ? { borderColor: "var(--hair)" } : undefined}
               >
                 <div className="eyebrow mb-0.5 text-[10px]">
-                  {message.role === "user" ? "You" : "Assistant"}
+                  {message.role === "user" ? "You" : assistantName}
                 </div>
                 {message.content}
               </div>
@@ -157,7 +158,7 @@ export function AssistantPanel({ configured, userId }: Props) {
                 aria-live="polite"
                 aria-busy="true"
               >
-                <div className="eyebrow mb-1 text-[10px]">Assistant</div>
+                <div className="eyebrow mb-1 text-[10px]">{assistantName}</div>
                 <div className="flex items-center gap-2 text-[12.5px] text-muted-foreground">
                   <Loader2 className="size-3.5 shrink-0 animate-spin" />
                   <span>{activityLabel ?? "Working…"}</span>
@@ -180,9 +181,9 @@ export function AssistantPanel({ configured, userId }: Props) {
         <Input
           value={input}
           onChange={(event) => setInput(event.target.value)}
-          placeholder="Ask the assistant…"
+          placeholder={`Ask ${assistantName}…`}
           disabled={isPending}
-          aria-label="Assistant message"
+          aria-label={`Message for ${assistantName}`}
           className="h-9"
         />
         <Button type="submit" size="sm" disabled={isPending || !input.trim()} aria-label="Send">