refactor: migrate from Biome to oxlint/oxfmt, remove contact form

- Replace Biome with oxlint + oxfmt (OXC toolchain) for linting and formatting
- Add .oxlintrc.json and .oxfmtrc.json configuration files
- Update VS Code settings and devcontainer to use oxc-vscode extension
- Remove contact form, Resend email integration, and related server action/schema
- Remove unused UI components (accordion, alert, card, tabs, toggle, etc.)

components/ui/separator.tsx

@@ -1,23 +1,16 @@
 "use client";
 
-import * as SeparatorPrimitive from "@radix-ui/react-separator";
-import type * as React from "react";
+import { Separator as SeparatorPrimitive } from "@base-ui/react/separator";
 
 import { cn } from "@/lib/utils";
 
-function Separator({
-  className,
-  orientation = "horizontal",
-  decorative = true,
-  ...props
-}: React.ComponentProps<typeof SeparatorPrimitive.Root>) {
+function Separator({ className, orientation = "horizontal", ...props }: SeparatorPrimitive.Props) {
   return (
-    <SeparatorPrimitive.Root
+    <SeparatorPrimitive
       data-slot="separator"
-      decorative={decorative}
       orientation={orientation}
       className={cn(
-        "shrink-0 bg-border data-[orientation=horizontal]:h-px data-[orientation=vertical]:h-full data-[orientation=horizontal]:w-full data-[orientation=vertical]:w-px",
+        "bg-border shrink-0 data-horizontal:h-px data-horizontal:w-full data-vertical:w-px data-vertical:self-stretch",
         className,
       )}
       {...props}