Add rename dialog, persist user identity, and send connect updates

[noahfraiture]

Motivation

• Provide a simple, pretty UI for users to change their display name and have that change reflected server-side via the existing connect flow.
• Persist a stable token and the chosen display name across sessions so reconnections keep identity and renames take effect immediately.

Description

• Added a daisyUI-styled rename modal in TopBar and exposed onRename/userName props to drive the UI, implemented in frontend/src/TopBar.tsx.
• Persist user token and name in localStorage, generate a stable token when missing, and surface token/userName to the app shell in frontend/src/main.tsx.
• Wire token and userName into the app and send a transport connect request when the socket is ready or the name changes, and use the active name for local message previews in frontend/src/App.tsx.

Testing

• Started the frontend dev server with pnpm --dir frontend dev which launched successfully (manual verification via server logs).
• Ran an automated Playwright script to open the running app, click the "Rename" button and take a screenshot which completed successfully and produced the rename-modal artifact.
• No unit tests were added or run as part of this change.

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Codex Task