Improve WebRTC streaming defaults and add client stream controls

[DjDeveloperr]

Summary

• Add UI controls for encoder, FPS, and stream quality, with local defaults favoring hardware H.264, 120 fps, and full-resolution quality.
• Make remote viewing default to software H.264 at 30 fps with the balanced profile, while still allowing manual overrides from the client.
• Tighten the server/native WebRTC pipeline for fresher frame delivery, safer encoder reconfiguration, and multi-viewer cleanup.
• Update stream-quality and health contracts, docs, and reliability scripts to reflect the new control surface and defaults.

Testing

• cargo fmt --manifest-path server/Cargo.toml --check
• cargo check --manifest-path server/Cargo.toml --quiet
• cargo test --manifest-path server/Cargo.toml transport::webrtc::tests --quiet
• TypeScript client typecheck and production client build passed
• Native CLI rebuild passed