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.

2 files changed, 102 insertions, 0 deletions

diff --git a/apps/web/src/types/animation.ts b/apps/web/src/types/animation.ts
new file mode 100644
index 00000000..b9ca91af
--- /dev/null
+++ b/apps/web/src/types/animation.ts
@@ -0,0 +1,89 @@
+export const ANIMATION_PROPERTY_PATHS = [
+	"transform.position.x",
+	"transform.position.y",
+	"transform.scale",
+	"transform.rotate",
+	"opacity",
+	"volume",
+] as const;
+
+export type AnimationPropertyPath = (typeof ANIMATION_PROPERTY_PATHS)[number];
+
+export type AnimationValueKind = "number" | "color" | "discrete";
+export type DiscreteValue = boolean | string;
+export type AnimationValue = number | string | boolean;
+
+export type NumberKeyframeInterpolation = "linear" | "hold";
+export type ColorKeyframeInterpolation = "linear" | "hold";
+export type DiscreteKeyframeInterpolation = "hold";
+export type AnimationInterpolation =
+	| NumberKeyframeInterpolation
+	| ColorKeyframeInterpolation
+	| DiscreteKeyframeInterpolation;
+
+interface BaseAnimationKeyframe<
+	TValue extends AnimationValue,
+	TInterpolation extends AnimationInterpolation,
+> {
+	id: string;
+	time: number; // relative to element start time
+	value: TValue;
+	interpolation: TInterpolation;
+}
+
+export interface NumberKeyframe
+	extends BaseAnimationKeyframe<number, NumberKeyframeInterpolation> {}
+
+export interface ColorKeyframe
+	extends BaseAnimationKeyframe<string, ColorKeyframeInterpolation> {}
+
+export interface DiscreteKeyframe
+	extends BaseAnimationKeyframe<DiscreteValue, DiscreteKeyframeInterpolation> {}
+
+export type AnimationKeyframe = NumberKeyframe | ColorKeyframe | DiscreteKeyframe;
+
+interface BaseAnimationChannel<
+	TValueKind extends AnimationValueKind,
+	TKeyframe extends AnimationKeyframe,
+> {
+	valueKind: TValueKind;
+	keyframes: TKeyframe[];
+}
+
+export interface NumberAnimationChannel
+	extends BaseAnimationChannel<"number", NumberKeyframe> {}
+
+export interface ColorAnimationChannel
+	extends BaseAnimationChannel<"color", ColorKeyframe> {}
+
+export interface DiscreteAnimationChannel
+	extends BaseAnimationChannel<"discrete", DiscreteKeyframe> {}
+
+export type AnimationChannel =
+	| NumberAnimationChannel
+	| ColorAnimationChannel
+	| DiscreteAnimationChannel;
+
+export type ElementAnimationChannelMap = Record<
+	string,
+	AnimationChannel | undefined
+>;
+
+export interface ElementAnimations {
+	channels: ElementAnimationChannelMap;
+}
+
+export interface ElementKeyframe {
+	propertyPath: AnimationPropertyPath;
+	id: string;
+	time: number;
+	value: AnimationValue;
+	interpolation: AnimationInterpolation;
+}
+
+export interface SelectedKeyframeRef {
+	trackId: string;
+	elementId: string;
+	propertyPath: AnimationPropertyPath;
+	keyframeId: string;
+}
diff --git a/apps/web/src/types/timeline.ts b/apps/web/src/types/timeline.ts
index 5a98bd31..26690458 100644
--- a/apps/web/src/types/timeline.ts
+++ b/apps/web/src/types/timeline.ts
@@ -1,4 +1,5 @@
 import type { BlendMode, Transform } from "./rendering";
+import type { ElementAnimations } from "./animation";
 
 export interface Bookmark {
 	time: number;
@@ -80,6 +81,7 @@ interface BaseTimelineElement {
 	startTime: number;
 	trimStart: number;
 	trimEnd: number;
+	animations?: ElementAnimations;
 }
 
 export interface VideoElement extends BaseTimelineElement {
@@ -136,6 +138,17 @@ export interface StickerElement extends BaseTimelineElement {
 	blendMode?: BlendMode;
 }
 
+export type VisualElement =
+	| VideoElement
+	| ImageElement
+	| TextElement
+	| StickerElement;
+
+export type ElementUpdatePatch =
+	| { transform: Transform }
+	| { opacity: number }
+	| { volume: number };
+
 export type TimelineElement =
 	| AudioElement
 	| VideoElement