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, 151 insertions, 0 deletions

diff --git a/apps/web/src/components/editor/panels/properties/hooks/use-keyframed-number-property.ts b/apps/web/src/components/editor/panels/properties/hooks/use-keyframed-number-property.ts
new file mode 100644
index 00000000..cd62ca75
--- /dev/null
+++ b/apps/web/src/components/editor/panels/properties/hooks/use-keyframed-number-property.ts
@@ -0,0 +1,151 @@
+import { useEditor } from "@/hooks/use-editor";
+import {
+	getKeyframeAtTime,
+	hasKeyframesForPath,
+	upsertElementKeyframe,
+} from "@/lib/animation";
+import type { AnimationPropertyPath, ElementAnimations } from "@/types/animation";
+import type { ElementUpdatePatch } from "@/types/timeline";
+import { usePropertyDraft } from "./use-property-draft";
+
+export function useKeyframedNumberProperty({
+	trackId,
+	elementId,
+	animations,
+	propertyPath,
+	localTime,
+	isPlayheadWithinElementRange,
+	displayValue,
+	parse,
+	valueAtPlayhead,
+	buildBaseUpdates,
+}: {
+	trackId: string;
+	elementId: string;
+	animations: ElementAnimations | undefined;
+	propertyPath: AnimationPropertyPath;
+	localTime: number;
+	isPlayheadWithinElementRange: boolean;
+	displayValue: string;
+	parse: (input: string) => number | null;
+	valueAtPlayhead: number;
+	buildBaseUpdates: ({ value }: { value: number }) => ElementUpdatePatch;
+}) {
+	const editor = useEditor();
+
+	const hasAnimatedKeyframes = hasKeyframesForPath({ animations, propertyPath });
+	const keyframeAtTime = isPlayheadWithinElementRange
+		? getKeyframeAtTime({ animations, propertyPath, time: localTime })
+		: null;
+	const keyframeIdAtTime = keyframeAtTime?.id ?? null;
+	const isKeyframedAtTime = keyframeAtTime !== null;
+	const shouldUseAnimatedChannel =
+		hasAnimatedKeyframes && isPlayheadWithinElementRange;
+
+	const previewValue = ({ value }: { value: number }) => {
+		if (shouldUseAnimatedChannel) {
+			editor.timeline.previewElements({
+				updates: [
+					{
+						trackId,
+						elementId,
+						updates: {
+							animations: upsertElementKeyframe({
+								animations,
+								propertyPath,
+								time: localTime,
+								value,
+							}),
+						},
+					},
+				],
+			});
+			return;
+		}
+
+		editor.timeline.previewElements({
+			updates: [
+				{
+					trackId,
+					elementId,
+					updates: buildBaseUpdates({ value }),
+				},
+			],
+		});
+	};
+
+	const propertyDraft = usePropertyDraft({
+		displayValue,
+		parse,
+		onPreview: (value) => previewValue({ value }),
+		onCommit: () => editor.timeline.commitPreview(),
+	});
+
+	const toggleKeyframe = () => {
+		if (!isPlayheadWithinElementRange) {
+			return;
+		}
+
+		if (keyframeIdAtTime) {
+			editor.timeline.removeKeyframes({
+				keyframes: [
+					{
+						trackId,
+						elementId,
+						propertyPath,
+						keyframeId: keyframeIdAtTime,
+					},
+				],
+			});
+			return;
+		}
+
+		editor.timeline.upsertKeyframes({
+			keyframes: [
+				{
+					trackId,
+					elementId,
+					propertyPath,
+					time: localTime,
+					value: valueAtPlayhead,
+				},
+			],
+		});
+	};
+
+	const commitValue = ({ value }: { value: number }) => {
+		if (shouldUseAnimatedChannel) {
+			editor.timeline.upsertKeyframes({
+				keyframes: [
+					{
+						trackId,
+						elementId,
+						propertyPath,
+						time: localTime,
+						value,
+					},
+				],
+			});
+			return;
+		}
+
+		editor.timeline.updateElements({
+			updates: [
+				{
+					trackId,
+					elementId,
+					updates: buildBaseUpdates({ value }),
+				},
+			],
+		});
+	};
+
+	return {
+		...propertyDraft,
+		hasAnimatedKeyframes,
+		isKeyframedAtTime,
+		keyframeIdAtTime,
+		toggleKeyframe,
+		commitValue,
+	};
+}