Initial commit: Western Shooter - Complete implementation

Retro western vertical shooter inspired by Gun.Smoke, built with
TypeScript and WebGL2. Features 3-direction shooting, vertical
scrolling, economy/shop loop, boss fights, and CRT shader effects.

Phases implemented:
- Phase 1: Engine skeleton (WebGL2 renderer, fixed timestep loop, input)
- Phase 2: Shooting identity (3-dir shooting, bullet pools, collision)
- Phase 3: Enemies & patterns (JSON waves, 4 enemy types, parallax bg)
- Phase 4: Economy loop (pickups, shop, upgrades, HUD)
- Phase 5: Boss system (3 bosses, wanted posters, multi-phase attacks)
- Phase 6: Shader layer (CRT effects, bloom, scanlines, screen shake)
- Phase 7: Performance (VAO batching, O(1) allocation, stress testing)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

src/rendering/framebuffer.ts

@@ -0,0 +1,72 @@
+export class Framebuffer {
+  public readonly framebuffer: WebGLFramebuffer;
+  public readonly texture: WebGLTexture;
+  public readonly width: number;
+  public readonly height: number;
+
+  constructor(gl: WebGL2RenderingContext, width: number, height: number) {
+    this.width = width;
+    this.height = height;
+
+    // Create texture for the framebuffer
+    const texture = gl.createTexture();
+    if (!texture) {
+      throw new Error('Failed to create framebuffer texture');
+    }
+    this.texture = texture;
+
+    gl.bindTexture(gl.TEXTURE_2D, texture);
+    gl.texImage2D(
+      gl.TEXTURE_2D,
+      0,
+      gl.RGBA,
+      width,
+      height,
+      0,
+      gl.RGBA,
+      gl.UNSIGNED_BYTE,
+      null
+    );
+
+    // Nearest-neighbor filtering for pixel-perfect upscaling
+    gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_MIN_FILTER, gl.NEAREST);
+    gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_MAG_FILTER, gl.NEAREST);
+    gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_WRAP_S, gl.CLAMP_TO_EDGE);
+    gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_WRAP_T, gl.CLAMP_TO_EDGE);
+
+    // Create framebuffer
+    const framebuffer = gl.createFramebuffer();
+    if (!framebuffer) {
+      throw new Error('Failed to create framebuffer');
+    }
+    this.framebuffer = framebuffer;
+
+    gl.bindFramebuffer(gl.FRAMEBUFFER, framebuffer);
+    gl.framebufferTexture2D(
+      gl.FRAMEBUFFER,
+      gl.COLOR_ATTACHMENT0,
+      gl.TEXTURE_2D,
+      texture,
+      0
+    );
+
+    // Check framebuffer status
+    const status = gl.checkFramebufferStatus(gl.FRAMEBUFFER);
+    if (status !== gl.FRAMEBUFFER_COMPLETE) {
+      throw new Error(`Framebuffer not complete: ${status}`);
+    }
+
+    // Unbind
+    gl.bindFramebuffer(gl.FRAMEBUFFER, null);
+    gl.bindTexture(gl.TEXTURE_2D, null);
+  }
+
+  bind(gl: WebGL2RenderingContext): void {
+    gl.bindFramebuffer(gl.FRAMEBUFFER, this.framebuffer);
+    gl.viewport(0, 0, this.width, this.height);
+  }
+
+  unbind(gl: WebGL2RenderingContext): void {
+    gl.bindFramebuffer(gl.FRAMEBUFFER, null);
+  }
+}