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.)

.devcontainer/devcontainer.json

@@ -5,7 +5,6 @@
   "customizations": {
     "vscode": {
       "settings": {
-        "editor.rulers": [120],
         "extensions.ignoreRecommendations": true,
         "git.allowForcePush": true,
         "git.autofetch": true,
@@ -21,16 +20,9 @@
         "typescript.tsserver.log": "off",
         "typescript.updateImportsOnFileMove.enabled": "always"
       },
-      "extensions": [
-        "biomejs.biome",
-        "bradlc.vscode-tailwindcss",
-        "unifiedjs.vscode-mdx"
-      ]
+      "extensions": ["bradlc.vscode-tailwindcss", "oxc.oxc-vscode", "unifiedjs.vscode-mdx"]
     }
   },
-  "tasks": {
-    "build": "pnpm install --frozen-lockfile && pnpm build"
-  },
   "forwardPorts": [3000],
   "containerEnv": {
     "CHECKPOINT_DISABLE": "1",