[codex] Add desktop Remote SSH support

[frizynn]

Summary

Adds desktop Remote SSH support so the local Electron app can connect to a DP Code server started on an SSH host, tunnel the backend WebSocket/HTTP connection, and open remote projects from the local UI.

Details

• Adds desktop IPC/contracts/preload APIs for Remote SSH connection status and local clipboard image reads.
• Starts the remote DP Code backend over SSH with key-based, non-interactive options, remote project cwd, health readiness, stderr diagnostics, and lifecycle cleanup.
• Adds localhost forwarding for the built-in browser, including HTTP/HTTPS/WS/WSS loopback URLs, fail-closed behavior on forwarding errors, and logical URL preservation in the address/history state.
• Adds local clipboard image paste fallback for Electron so pasted screenshots/images still attach while connected to a remote backend.
• Adds focused tests for remote startup command construction and readiness handling.

Validation

• git diff --cached --check
• npx -y -p node@24.13.1 -p bun@1.3.9 -c 'cd apps/desktop && bun run test'
• npx -y -p node@24.13.1 -p bun@1.3.9 -c 'cd apps/web && bun run test'
• npx -y -p node@24.13.1 -p bun@1.3.9 -c 'bun run build:desktop'
• Local SSH smoke for the remote backend manager and browser port forwarder during implementation

[frizynn]

Closing this draft PR.