feat(journal): implement session management UI components

Add a suite of dialogs and header components to manage journal
sessions, including:

- ConnectDialog for joining sessions with name and role selection
- CreateSessionDialog for starting new sessions
- InviteDialog for generating and copying player invite links
- SessionDropdown for switching between sessions (GM only)
- JournalHeader for displaying connection status and user info

src/components/journal/index.ts

@@ -37,6 +37,11 @@ export type {
 // UI components
 export { JournalPanel } from "./JournalPanel";
 export type { JournalPanelProps } from "./JournalPanel";
+export { JournalHeader } from "./JournalHeader";
+export { ConnectDialog } from "./ConnectDialog";
+export { InviteDialog } from "./InviteDialog";
+export { SessionDropdown } from "./SessionDropdown";
+export { CreateSessionDialog } from "./CreateSessionDialog";
 export { ConnectionBar } from "./ConnectionBar";
 export { StreamView } from "./StreamView";
 export { StreamMessageCard } from "./StreamMessage";