perf(stream): Adaptive polling, diagnostics optimization, and lag classification

[zortos293]

Summary

Optimizes streaming performance through adaptive input polling, decoupled diagnostics, and real-time lag classification.

Performance Improvements

Adaptive polling

• Gamepad polling now dynamically adjusts between 4ms (active controllers, visible document) and 100ms (idle or no controllers)
• Microphone meter uses 33ms timer interval instead of per-frame rAF loop, with reduced analyser FFT size (256)

Decoupled diagnostics

• Moved stream diagnostics to external store using useSyncExternalStore to eliminate React re-renders from 500ms stats polling
• StreamView and App subscribe directly to the store instead of props drilling stats through the component tree

Lag classification

• Added comprehensive lag reason analyzer detecting: network congestion, decoder saturation, input backpressure, and render bottlenecks
• Classifies signals into reasons: network, decoder, input_backpressure, render, stable, or unknown
• Surfaces lag reason and detail strings in the in-game stats overlay for actionable feedback

Changes

src/renderer/src/gfn/webrtcClient.ts

• Added StreamLagReason type and lagReason/lagReasonDetail to StreamDiagnostics
• Implemented classifyLagReason() for automatic bottleneck detection
• Converted gamepad polling to adaptive via scheduleGamepadPolling() and getGamepadPollIntervalMs()
• Integrated lag classification into stats collection loop

src/renderer/src/utils/streamDiagnosticsStore.ts (new)

• External store for stream diagnostics with createStreamDiagnosticsStore() and useStreamDiagnosticsStore() hook
• Uses useSyncExternalStore for efficient subscriptions without React re-renders

src/renderer/src/App.tsx

• Replaced setDiagnostics state with diagnosticsStore external store
• Removed stats prop from StreamView; components now subscribe directly

src/renderer/src/components/StreamView.tsx

• Subscribes to diagnostics via useStreamDiagnosticsStore() hook
• Added lag reason display in stats HUD with color-coded badges
• Switched microphone meter to 33ms setTimeout loop with reduced FFT size

src/renderer/src/components/StatsOverlay.tsx

• Added lag reason indicator in overlay for compact diagnostics view