feat(journal): delete sessions from the ui

Add a confirmation dialog that spells out the removal is irreversible, and expose delete from the GM session dropdown and the lobby session list.

src/components/journal/JournalHeader.tsx

@@ -8,6 +8,7 @@ import { SessionDropdown } from "./SessionDropdown";
 interface JournalHeaderProps {
   onClose: () => void;
   onCreateSession: () => void;
+  onDeleteSession: (id: string, name: string) => void;
 }
 
 export const JournalHeader: Component<JournalHeaderProps> = (props) => {
@@ -54,7 +55,10 @@ export const JournalHeader: Component<JournalHeaderProps> = (props) => {
             </p>
             {/* Clickable subtitle — session dropdown (GM only) */}
             <Show when={stream.myRole === "gm"}>
-              <SessionDropdown onCreate={props.onCreateSession} />
+              <SessionDropdown
+                onCreate={props.onCreateSession}
+                onDelete={props.onDeleteSession}
+              />
             </Show>
           </div>
         </Show>