fix(menu): route Cmd+N to new chat session

[kagura-agent]

Problem

Pressing Cmd+N (File → New Chat) opens a blank window because menu.ts sends navigate('/chat'), but no /chat route exists in React Router.

The same issue affects Navigate → Chat (Cmd+2).

Fix

• File → New Chat (Cmd+N): Send new new-chat IPC event instead of navigate('/chat'). Renderer listens and calls newSession() + navigate('/') (matching Sidebar behavior).
• Navigate → Chat (Cmd+2): Change navigate('/chat') to navigate('/').

Testing

• All 346 tests pass
• Verified menu IPC events route correctly

Closes #720

[chatgpt-codex-connector]

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[chatgpt-codex-connector]

Allowlist new IPC channel before subscribing

Subscribing to window.electron.ipcRenderer.on('new-chat', ...) will throw at runtime because the preload bridge only permits channels listed in electron/preload/index.ts, and 'new-chat' is not in that allowlist (on() throws Invalid IPC channel for unknown values). This means the new effect can fail during app startup and the Cmd/Ctrl+N flow never gets a listener in production builds unless the preload allowlist is updated to include this event.

Useful? React with 👍 / 👎.