fix(ppu): call present() at the end of each frame to display output

src/Frontend/Wasm/WasmFramebuffer.php

@@ -125,4 +125,15 @@ public function getHeight(): int
     {
         return self::HEIGHT;
     }
+
+    /**
+     * Present the framebuffer.
+     *
+     * For WASM, this is a no-op since JavaScript explicitly polls
+     * for pixel data via getPixelsRGBA() in the render loop.
+     */
+    public function present(): void
+    {
+        // No-op for WASM - JavaScript polls for pixel data
+    }
 }

src/Ppu/ArrayFramebuffer.php

@@ -43,4 +43,10 @@ public function clear(): void
             $this->buffer[$y] = array_fill(0, self::WIDTH, $white);
         }
     }
+
+    public function present(): void
+    {
+        // No-op for array framebuffer (used for testing)
+        // Actual rendering implementations (CLI, WASM) should override this
+    }
 }

src/Ppu/FramebufferInterface.php

@@ -34,4 +34,12 @@ public function getFramebuffer(): array;
      * Clear the framebuffer (typically to white).
      */
     public function clear(): void;
+
+    /**
+     * Present the framebuffer (display/render the current frame).
+     *
+     * Called by the PPU at the end of each frame to signal that
+     * the frame is complete and ready to be displayed.
+     */
+    public function present(): void;
 }

src/Ppu/Ppu.php

@@ -191,6 +191,9 @@ private function stepVBlank(): void
                 $this->ly = 0;
                 $this->updateLycCoincidence();
                 $this->setMode(PpuMode::OamSearch);
+
+                // Frame complete - present the framebuffer
+                $this->framebuffer->present();
             }
         }
     }