feat: introduce WebGL effects system and Blur effect

This implements the foundational architecture for video effects, starting with a multi-pass WebGL rendering pipeline and a customizable Gaussian Blur effect.

Key changes:
- WebGL Engine: Added `raw-loader` for `.glsl` shaders, multi-pass framebuffer rendering, and live offscreen canvas previews.
- Node Architecture: Replaced hardcoded background blur with `CompositeEffectNode` and added `EffectLayerNode` to apply effects to specific visual elements.
- Timeline & DND: Added a new `effect` track type. Upgraded drag-and-drop to support dropping effects directly onto the timeline. Consolidated track constants into a cleaner `TRACK_CONFIG`.
- UI/UX: Added an Effects tab in the assets panel with live previews. Added an Effect Properties panel with sliders and inputs for fine-tuning parameters.
- Data Model: Added `sourceDuration` to video and audio elements, and wrote a v8 storage migration to update existing projects to the new schema.
- Docs: Added `CHANGELOG.md` tracking v0.1.0 and v0.2.0, plus `docs/effects-renderer.md` to document the new WebGL pipeline.

apps/web/src/services/renderer/nodes/composite-effect-node.ts

@@ -0,0 +1,77 @@
+import type { CanvasRenderer } from "../canvas-renderer";
+import { createOffscreenCanvas } from "../canvas-utils";
+import { getEffect } from "@/lib/effects";
+import type { EffectParamValues } from "@/types/effects";
+import { BaseNode } from "./base-node";
+import { webglEffectRenderer } from "../webgl-effect-renderer";
+
+export type CompositeEffectNodeParams = {
+	contentNodes: BaseNode[];
+	effectType: string;
+	effectParams: EffectParamValues;
+	scale: number;
+};
+
+export class CompositeEffectNode extends BaseNode<CompositeEffectNodeParams> {
+	async render({
+		renderer,
+		time,
+	}: {
+		renderer: CanvasRenderer;
+		time: number;
+	}): Promise<void> {
+		const offscreen = createOffscreenCanvas({
+			width: renderer.width,
+			height: renderer.height,
+		});
+		const offscreenCtx = offscreen.getContext("2d") as OffscreenCanvasRenderingContext2D | null;
+		if (!offscreenCtx) {
+			throw new Error("failed to get offscreen canvas context");
+		}
+
+		const originalContext = renderer.context;
+		renderer.context = offscreenCtx;
+
+		for (const node of this.params.contentNodes) {
+			await node.render({ renderer, time });
+		}
+
+		renderer.context = originalContext;
+
+		const effectDefinition = getEffect({ effectType: this.params.effectType });
+		const scale = this.params.scale;
+		const scaledWidth = renderer.width * scale;
+		const scaledHeight = renderer.height * scale;
+		const offsetX = (renderer.width - scaledWidth) / 2;
+		const offsetY = (renderer.height - scaledHeight) / 2;
+
+		const passes = effectDefinition.renderer.passes.map((pass) => ({
+			fragmentShader: pass.fragmentShader,
+			uniforms: pass.uniforms({
+				effectParams: this.params.effectParams,
+				width: renderer.width,
+				height: renderer.height,
+			}),
+		}));
+		const effectResult = webglEffectRenderer.applyEffect({
+			source: offscreen as CanvasImageSource,
+			width: renderer.width,
+			height: renderer.height,
+			passes,
+		});
+
+		renderer.context.save();
+		renderer.context.drawImage(
+			effectResult,
+			0,
+			0,
+			renderer.width,
+			renderer.height,
+			offsetX,
+			offsetY,
+			scaledWidth,
+			scaledHeight,
+		);
+		renderer.context.restore();
+	}
+}