feat(webgl): Wire up WEBGL_GAL test harness with proper canvas setup

- Add wasm_stubs.cpp with WASM-specific stub implementations for
  COLOR4D::BLACK/WHITE, GLU tesselator, PGM_BASE, and other KiCad
  dependencies
- Update Makefile to include KiCad sources (GAL base class, display
  options, HiDPI canvas) and test scenarios
- Fix kiglew.h to define GLEW guard (__glew_h__) preventing conflicts
  with Emscripten's GLEW header
- Update test HTML to create canvas before module load (MODULARIZE
  requires passing canvas in Module config, not preRun)
- Update Playwright tests to find canvas elements correctly
- Add #window-container for wxWidgets GL canvas support

Build produces 8.4MB WASM with full WEBGL_GAL implementation.
Tests pass but rendering still shows dark output (debugging in progress).

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

tests/e2e/gal-webgl.spec.ts

@@ -96,9 +96,38 @@ test.describe('GAL WebGL Regression Tests', () => {
       // Wait for rendering to complete
       await page.waitForTimeout(100);
 
-      // Get the canvas element and take a screenshot of just the canvas
-      const canvas = await page.locator('#canvas');
-      await expect(canvas).toBeVisible();
+      // Debug: list all canvases on the page
+      const canvasInfo = await page.evaluate(() => {
+        const canvases = document.querySelectorAll('canvas');
+        const windowContainer = document.getElementById('window-container');
+        return {
+          canvases: Array.from(canvases).map(c => ({
+            id: c.id,
+            className: c.className,
+            width: c.width,
+            height: c.height,
+            display: window.getComputedStyle(c).display,
+            parentId: c.parentElement?.id
+          })),
+          windowContainerChildren: windowContainer?.children.length || 0,
+          allElements: document.querySelectorAll('#window-container *').length
+        };
+      });
+      console.log('Canvas debug:', JSON.stringify(canvasInfo, null, 2));
+
+      // Get the canvas element
+      // First try GL canvas, fall back to main canvas
+      let canvas = page.locator('.gl-canvas').first();
+      if (!(await canvas.count())) {
+        canvas = page.locator('#canvas');
+      }
+
+      // If still no canvas, use first available
+      if (!(await canvas.count())) {
+        canvas = page.locator('canvas').first();
+      }
+
+      await expect(canvas).toBeVisible({ timeout: 5000 });
 
       // Screenshot the canvas (matching native 800x600 output)
       const screenshotPath = path.join(OUTPUT_DIR, `gal-${scenarioName}.png`);