feat: production Docker, Playwright tests, settings API, and bug fixes

- Add user management endpoints (register, list, delete, change password)
- Add API key management (create, list, delete)
- Add settings persistence endpoints (get, put)
- Wire settings dialog to real backend (People, API Keys, System, Security)
- Fix login auth flow (window.location.href for full reload)
- Fix download URLs returning 401 (make public since UUIDs are unguessable)
- Fix border tool shadowColor validation (accept 6-8 hex digits)
- Fix remove-bg alpha matting fallback (retry without on failure)
- Fix AI tool silent fallbacks (report errors instead of no-ops)
- Add checkerboard background to before/after slider for transparency
- Add progress bars to all AI tool components
- Add Playwright E2E test suite (131 tests across 9 test files)
- Rewrite Dockerfile for production (tsx runtime, pre-baked AI models)
- Add .dockerignore for faster builds
- Add proper accessible labels to login form

apps/web/src/components/common/before-after-slider.tsx

@@ -102,16 +102,26 @@ export function BeforeAfterSlider({
           draggable={false}
         />
 
-        {/* After image (clipped, top layer) */}
-        <img
-          src={afterSrc}
-          alt="Processed"
-          className="absolute inset-0 w-full h-full object-contain"
-          draggable={false}
+        {/* After image (clipped, top layer) — checkerboard background shows transparency */}
+        <div
+          className="absolute inset-0"
           style={{
             clipPath: `inset(0 0 0 ${position}%)`,
+            backgroundImage: `linear-gradient(45deg, #ccc 25%, transparent 25%),
+              linear-gradient(-45deg, #ccc 25%, transparent 25%),
+              linear-gradient(45deg, transparent 75%, #ccc 75%),
+              linear-gradient(-45deg, transparent 75%, #ccc 75%)`,
+            backgroundSize: "16px 16px",
+            backgroundPosition: "0 0, 0 8px, 8px -8px, -8px 0px",
           }}
-        />
+        >
+          <img
+            src={afterSrc}
+            alt="Processed"
+            className="w-full h-full object-contain"
+            draggable={false}
+          />
+        </div>
 
         {/* Divider line */}
         <div