Renderer: add bezier and quadratic curve path methods

[obiot]

Summary

Add bezierCurveTo() and quadraticCurveTo() path methods to the renderer API, matching the Canvas 2D API.

Requirements

• bezierCurveTo(cp1x, cp1y, cp2x, cp2y, x, y) — cubic bezier curve
• quadraticCurveTo(cpx, cpy, x, y) — quadratic bezier curve
• Both should work within beginPath() / closePath() / stroke() / fill() flow
• Available on both Canvas and WebGL renderers

Use Cases

• Particle trails and swoosh effects
• Path-based movement visualization
• UI bezier animations and transitions
• Custom shape drawing (speech bubbles, organic shapes)

Approach

Canvas renderer: Direct pass-through to ctx.bezierCurveTo() / ctx.quadraticCurveTo().

WebGL renderer: Tessellate the curve into line segments using De Casteljau's algorithm, then feed the resulting points into the existing primitive batcher. A configurable segment count (or adaptive based on curve length) controls quality vs. performance. The _drawPoints array already used by lineTo() can accumulate the tessellated points.

Refactor: Extract #generateTriangleFan from webgl_renderer.js into a new tessellation.js utility module. This module would centralize all geometry tessellation helpers (triangle fans, bezier/quadratic curve subdivision, etc.) for reuse across the renderer and future features.