feat: implement keyframe animation system

Add keyframe support for transform, opacity, and volume properties.
Includes animation engine (interpolation, mutations, resolvers), timeline
markers with selection/snapping, properties panel toggles, keyframe-aware
renderer, and full undo/redo command support.

Also refactor element command constructors to object params, extract
timeline pixel math to pixel-utils.ts, and update cursor rules.

1 files changed, 111 insertions, 0 deletions

diff --git a/apps/web/src/lib/animation/resolve.ts b/apps/web/src/lib/animation/resolve.ts
new file mode 100644
index 00000000..58f292b1
--- /dev/null
+++ b/apps/web/src/lib/animation/resolve.ts
@@ -0,0 +1,111 @@
+import type { ElementAnimations } from "@/types/animation";
+import type { Transform } from "@/types/timeline";
+import { getNumberChannelValueAtTime } from "./interpolation";
+import { getNumberChannelForPath } from "./number-channel";
+
+export function getElementLocalTime({
+	timelineTime,
+	elementStartTime,
+	elementDuration,
+}: {
+	timelineTime: number;
+	elementStartTime: number;
+	elementDuration: number;
+}): number {
+	const localTime = timelineTime - elementStartTime;
+	if (localTime <= 0) {
+		return 0;
+	}
+
+	if (localTime >= elementDuration) {
+		return elementDuration;
+	}
+
+	return localTime;
+}
+
+export function resolveTransformAtTime({
+	baseTransform,
+	animations,
+	localTime,
+}: {
+	baseTransform: Transform;
+	animations: ElementAnimations | undefined;
+	localTime: number;
+}): Transform {
+	const safeLocalTime = Math.max(0, localTime);
+	return {
+		position: {
+			x: getNumberChannelValueAtTime({
+				channel: getNumberChannelForPath({
+					animations,
+					propertyPath: "transform.position.x",
+				}),
+				time: safeLocalTime,
+				fallbackValue: baseTransform.position.x,
+			}),
+			y: getNumberChannelValueAtTime({
+				channel: getNumberChannelForPath({
+					animations,
+					propertyPath: "transform.position.y",
+				}),
+				time: safeLocalTime,
+				fallbackValue: baseTransform.position.y,
+			}),
+		},
+		scale: getNumberChannelValueAtTime({
+			channel: getNumberChannelForPath({
+				animations,
+				propertyPath: "transform.scale",
+			}),
+			time: safeLocalTime,
+			fallbackValue: baseTransform.scale,
+		}),
+		rotate: getNumberChannelValueAtTime({
+			channel: getNumberChannelForPath({
+				animations,
+				propertyPath: "transform.rotate",
+			}),
+			time: safeLocalTime,
+			fallbackValue: baseTransform.rotate,
+		}),
+	};
+}
+
+export function resolveOpacityAtTime({
+	baseOpacity,
+	animations,
+	localTime,
+}: {
+	baseOpacity: number;
+	animations: ElementAnimations | undefined;
+	localTime: number;
+}): number {
+	return getNumberChannelValueAtTime({
+		channel: getNumberChannelForPath({
+			animations,
+			propertyPath: "opacity",
+		}),
+		time: Math.max(0, localTime),
+		fallbackValue: baseOpacity,
+	});
+}
+
+export function resolveVolumeAtTime({
+	baseVolume,
+	animations,
+	localTime,
+}: {
+	baseVolume: number;
+	animations: ElementAnimations | undefined;
+	localTime: number;
+}): number {
+	return getNumberChannelValueAtTime({
+		channel: getNumberChannelForPath({
+			animations,
+			propertyPath: "volume",
+		}),
+		time: Math.max(0, localTime),
+		fallbackValue: baseVolume,
+	});
+}