fix(browser): persist session storage across restarts, prevent tab unmount on navigation, increase tunnel connection limit

[4Liberty]

Summary

This PR resolves three interconnected issues affecting OpenCode's embedded browser pane:

1. Sessions/Cookies Wiped on Reload: The browser pane previously generated an ephemeral UUID partition (opencode-browser-${crypto.randomUUID()}), causing all cookies, logins, IndexedDB, and Local Storage to be discarded on app restart or pane re-attachment. By switching to partition: "persist:opencode-browser", Electron persists session cookies and authentication state across restarts in the application's persistent partition directory.
2. Background Tabs Destroyed & Reloaded: Main frame navigation in the host window previously triggered navigate -> close(entry) -> page.dispose(), causing the browser pane to be destroyed and fully reloaded from scratch upon refocus. We retain lifecycle cleanup on actual window destruction while preventing spurious unmounts on internal window routing.
3. Tunnel Bottleneck on Rich Assets: The RPC network proxy enforced an aggressive hard limit of 64 concurrent sockets (sockets.size >= 64), causing asset-rich pages to stall or throw 502 connection limit errors. We increase the connection ceiling to 512.

Verification

• Verified Electron session persistence: session cookies and Local Storage are successfully retained across app restarts in Partitions/opencode-browser.
• Tested page stability across backgrounding and navigation.
• Verified asset loading concurrency under heavy network requests.

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