Implement standalone Rust remote desktop backend

[jdvmi00]

Remote sessions currently depend on Hypertile’s layout controller. This adds an independent Rust/Tokio daemon, CLI, and per-client supervisor so Moonlight windows can move and resize without stream restart or placement correction. Each computer has serialized host operations, durable intent/recovery, process ownership checks, and restart adoption.

Preserve the tested Python macOS and Windows recovery adapters behind one-shot helpers; leave video, audio, input, and hardware decoding in Moonlight/Sunshine. Document Qt 6/QML as the separate future manager UI, source provenance, configuration, handoff constraints, and measured backend overhead. No live installation, host changes, graphical UI, packaging, or promotion to main is included.

Validation:

• Rust format/Clippy, debug/release builds, and 5 Rust tests passed locally.
• 29 Python repository/host tests and 13 real-backend integration tests passed with isolated fake clients/hosts.
• Empty release daemon: 3,968 KiB RSS; median status socket round trip 0.046 ms. These are local samples, not streaming latency measurements.
• CI runs Linux backend tests, portable Windows checks, and the native PowerShell display policy/journal suite. All three must pass before rebase merge into develop.