telemetry: 6 audit gap fixes + composition-rollup ingestion

[AIEraDev]

Implements all 6 telemetry audit gaps plus composition-rollup ingestion. Two commits, 18 files, passes pre-commit TS check and cargo check.

Commit 1 — Fill 6 audit gaps

Fix 1 — Audio seek & underrun telemetry

• seek_count + seek_latency_total_us atomics on NativeAudioClock; seek() records count and cumulative latency
• total_underruns() accessor on AudioRingBufferConsumer
• TS NativeAudioStatus gains seekCount, seekLatencyTotalUs, clockFreshnessUs?, medianCallbackIntervalUs?
• useAudioSyncEngine derives window-delta seekCount/seekP95Ms per 5 s sample

Fix 2 — Filmstrip tile telemetry reaches NDJSON

• perfLogService calls filmstripTelemetry.getSummary() + clear() every flush interval as "filmstrip-rollup"; final window flushed at session close

Fix 3 — Real Rust-side export timing

• finalize_video_export returns ExportTimings (ffmpegFinalizeMs, avgFrameWriteMs, p95)
• videoExport.ts replaces 60%/40% ratio placeholders with real measurements

Fix 4 — Frontend A/V sync stats persist to NDJSON

• uiPlayheadDrift, playheadPaintJitter, seekUserLatency drained into "frontend-av-sync" entries each flush interval
• startSyncMetricsFlushLoop switched to non-destructive snapshot() to avoid racing with the drain

Fix 5 — Timeline edit telemetry

• Every split, move, and trim emits a "timeline-edit" NDJSON entry with operation type, clip ID, from/to positions, success flag, wall-clock duration

Fix 6 — Real process RSS replaces hard-coded peakRamMb

• get_process_memory_mb Tauri command via libc::getrusage(RUSAGE_SELF)
• perfLogService polls it every flush interval, tracks rolling peak; all 8 placeholder sites updated

Commit 2 — Composition-rollup ingestion + sticker-rollup DB fix

App side:

• TelemetryCompositionSample + TelemetryCompositionMetrics types with p50/p95/p99 per layer type
• CompositionWindowAccumulator (bounded 1000 samples, one rollup per window)
• recordCompositionSample() called from NativeProgramPreview per evaluated render scene using scene.visualLayers — active layers only, never clip metadata
• "composition-rollup" PerfLogKind routing

API side (performanceStorageService + types):

• CompositionMetrics interface + compositionMetrics? on PerformanceEventPayload
• "sticker-rollup" and "composition-rollup" added to the DB ingestion whitelist in both ingestSession() and getSessionEvents()
• Sticker rollups were previously archived in R2 but silently excluded from session_perf_logs JSONB — fixed

Tests: telemetryCollector.test.ts 16/16 pass

No schema migration needed.