feat(admin): implement initial admin dashboard and member management

This commit introduces the foundational structure for the admin dashboard, focusing on the member management feature.
Key additions include:

- A new page at `/admin/manage/members` to display and manage members.
- An `AddModal` component with a comprehensive form for creating new members, featuring validation with Zod and input
masking.
- A reusable `PhoneInput` component with country code selection, backed by a new `useCountries` composable and a full
country dataset.
- A custom, user-friendly global error page (`error.vue`) to handle application errors gracefully.
- Updated dashboard sidebar navigation to include the new member management section.
- Added recommended VS Code extensions and settings to improve developer experience.

.vscode/settings.json

@@ -19,5 +19,6 @@
   ],
   "tailwindCSS.experimental.classRegex": [
     ["ui:\\s*{([^)]*)\\s*}", "(?:'|\"|`)([^']*)(?:'|\"|`)"]
-  ]
+  ],
+  "css.lint.unknownAtRules": "ignore"
 }