Raylux 0.30.3: a faster write path

Performance work on the gateway, and fixes in the designer and the plant-floor client.

Performance

• The gateway's write path is about 44% faster — 66,900 to 96,200 values per second, measured.
• Tag updates now reach only the screens actually subscribed to them, instead of every connected client on every change. The cost of delivering a change no longer grows with how many operator screens are open.

Fixes

• A screen with no recognised layout is now reported as a problem rather than silently passing validation — which is how a malformed screen could hide a broken binding.
• Switching workspace no longer leaves the previous workspace's panels on screen.
• An unrecognised display mode on a plant-floor panel now presents full-screen instead of falling back to a desktop window — the one fallback a commissioned panel must never take.