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, 67 insertions, 0 deletions

diff --git a/apps/web/src/lib/animation/keyframe-query.ts b/apps/web/src/lib/animation/keyframe-query.ts
new file mode 100644
index 00000000..f3288e7a
--- /dev/null
+++ b/apps/web/src/lib/animation/keyframe-query.ts
@@ -0,0 +1,67 @@
+import { TIME_EPSILON_SECONDS } from "@/constants/animation-constants";
+import type {
+	AnimationPropertyPath,
+	ElementAnimations,
+	ElementKeyframe,
+} from "@/types/animation";
+
+export function getElementKeyframes({
+	animations,
+}: {
+	animations: ElementAnimations | undefined;
+}): ElementKeyframe[] {
+	if (!animations) {
+		return [];
+	}
+
+	return Object.entries(animations.channels).flatMap(
+		([propertyPath, channel]) => {
+			if (!channel || channel.keyframes.length === 0) {
+				return [];
+			}
+
+			return channel.keyframes.map((keyframe) => ({
+				propertyPath: propertyPath as AnimationPropertyPath,
+				id: keyframe.id,
+				time: keyframe.time,
+				value: keyframe.value,
+				interpolation: keyframe.interpolation,
+			}));
+		},
+	);
+}
+
+export function hasKeyframesForPath({
+	animations,
+	propertyPath,
+}: {
+	animations: ElementAnimations | undefined;
+	propertyPath: AnimationPropertyPath;
+}): boolean {
+	const channel = animations?.channels[propertyPath];
+	return Boolean(channel && channel.keyframes.length > 0);
+}
+
+export function getKeyframeAtTime({
+	animations,
+	propertyPath,
+	time,
+}: {
+	animations: ElementAnimations | undefined;
+	propertyPath: AnimationPropertyPath;
+	time: number;
+}): ElementKeyframe | null {
+	const channel = animations?.channels[propertyPath];
+	if (!channel || channel.keyframes.length === 0) return null;
+	const keyframe = channel.keyframes.find(
+		(kf) => Math.abs(kf.time - time) <= TIME_EPSILON_SECONDS,
+	);
+	if (!keyframe) return null;
+	return {
+		propertyPath,
+		id: keyframe.id,
+		time: keyframe.time,
+		value: keyframe.value,
+		interpolation: keyframe.interpolation,
+	};
+}