feat: ripple-extend resize, timeline filmstrip, export hardening

Yesterday's verified web session (gates green: 316 tests, tsc, build):
- ripple-extend pushes right-hand chain on static-element resize
- per-position video filmstrip thumbnails with zoom-adaptive density
- fps-aware export bitrate, 2s keyframes, even-dim export canvas
- freeze frame uses fixed 3s duration, prompt removed

1 files changed, 22 insertions, 0 deletions

diff --git a/apps/web/src/services/renderer/export-encoding.ts b/apps/web/src/services/renderer/export-encoding.ts
new file mode 100644
index 00000000..cc333ea4
--- /dev/null
+++ b/apps/web/src/services/renderer/export-encoding.ts
@@ -0,0 +1,22 @@
+import type { ExportQuality } from "@/export";
+
+const videoBitsPerPixelFrame: Record<ExportQuality, number> = {
+	low: 0.05,
+	medium: 0.1,
+	high: 0.2,
+	very_high: 0.4,
+};
+
+export function computeVideoBitrate({
+	width,
+	height,
+	fps,
+	quality,
+}: {
+	width: number;
+	height: number;
+	fps: number;
+	quality: ExportQuality;
+}): number {
+	return Math.round(width * height * fps * videoBitsPerPixelFrame[quality]);
+}