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, 37 insertions, 0 deletions

diff --git a/apps/web/src/core/managers/selection-manager.ts b/apps/web/src/core/managers/selection-manager.ts
index fa6a02bf..e4295c11 100644
--- a/apps/web/src/core/managers/selection-manager.ts
+++ b/apps/web/src/core/managers/selection-manager.ts
@@ -1,9 +1,12 @@
 import type { EditorCore } from "@/core";
+import type { SelectedKeyframeRef } from "@/types/animation";
 
 type ElementRef = { trackId: string; elementId: string };
 
 export class SelectionManager {
 	private selectedElements: ElementRef[] = [];
+	private selectedKeyframes: SelectedKeyframeRef[] = [];
+	private keyframeSelectionAnchor: SelectedKeyframeRef | null = null;
 	private listeners = new Set<() => void>();
 
 	constructor(editor: EditorCore) {
@@ -14,13 +17,47 @@ export class SelectionManager {
 		return this.selectedElements;
 	}
 
+	getSelectedKeyframes(): SelectedKeyframeRef[] {
+		return this.selectedKeyframes;
+	}
+
+	getKeyframeSelectionAnchor(): SelectedKeyframeRef | null {
+		return this.keyframeSelectionAnchor;
+	}
+
 	setSelectedElements({ elements }: { elements: ElementRef[] }): void {
 		this.selectedElements = elements;
+		this.selectedKeyframes = [];
+		this.keyframeSelectionAnchor = null;
+		this.notify();
+	}
+
+	setSelectedKeyframes({
+		keyframes,
+		anchorKeyframe,
+	}: {
+		keyframes: SelectedKeyframeRef[];
+		anchorKeyframe?: SelectedKeyframeRef | null;
+	}): void {
+		this.selectedKeyframes = keyframes;
+		if (anchorKeyframe !== undefined) {
+			this.keyframeSelectionAnchor = anchorKeyframe;
+		} else if (keyframes.length === 0) {
+			this.keyframeSelectionAnchor = null;
+		}
 		this.notify();
 	}
 
 	clearSelection(): void {
 		this.selectedElements = [];
+		this.selectedKeyframes = [];
+		this.keyframeSelectionAnchor = null;
+		this.notify();
+	}
+
+	clearKeyframeSelection(): void {
+		this.selectedKeyframes = [];
+		this.keyframeSelectionAnchor = null;
 		this.notify();
 	}