Add unified Node app construction with config mismatch guards

[RtlZeroMemory]

Summary

• add createNodeApp in @rezi-ui/node as the recommended construction path with one shared config surface for core and backend knobs
• add deterministic config guards for cursor protocol pairing, event buffer cap alignment, and fps cap alignment
• enforce fps precedence by treating fpsCap as canonical and requiring nativeConfig.targetFps or nativeConfig.target_fps to match
• expose backend capability markers so createApp can fail fast when app/backend settings diverge
• add regression tests for cursor mismatch (both directions), maxEventBytes mismatch, fps rules, and invalid event byte count handling
• update Node docs/examples to prefer createNodeApp and document guard behavior

Why

Users could previously configure related runtime knobs in multiple places and accidentally combine incompatible values. This change makes the default Node path safe by construction and adds deterministic, actionable failures for advanced/manual wiring paths.