docs: update documentation for v0.4.0 release

- Update README.md with v0.4.0 features and screenshots placeholders
- Update architecture.md with v0.4.0 implementation status
- Update progress.md marking all 27 tasks as completed
- Create CHANGELOG.md with complete release notes
- Add v0.4.0 frontend components and hooks

frontend/src/components/ui/badge-variants.ts

@@ -0,0 +1,21 @@
+import { cva } from "class-variance-authority"
+
+export const badgeVariants = cva(
+  "inline-flex items-center rounded-full border px-2.5 py-0.5 text-xs font-semibold transition-colors focus:outline-none focus:ring-2 focus:ring-ring focus:ring-offset-2",
+  {
+    variants: {
+      variant: {
+        default:
+          "border-transparent bg-primary text-primary-foreground hover:bg-primary/80",
+        secondary:
+          "border-transparent bg-secondary text-secondary-foreground hover:bg-secondary/80",
+        destructive:
+          "border-transparent bg-destructive text-destructive-foreground hover:bg-destructive/80",
+        outline: "text-foreground",
+      },
+    },
+    defaultVariants: {
+      variant: "default",
+    },
+  }
+)