feat: initialize thoughts-frontend with Next.js, TypeScript, and ESLint

- Add ESLint configuration for Next.js and TypeScript support.
- Create Next.js configuration file with standalone output option.
- Initialize package.json with scripts for development, build, and linting.
- Set up PostCSS configuration for Tailwind CSS.
- Add SVG assets for UI components.
- Create TypeScript configuration for strict type checking and module resolution.

thoughts-backend/app/src/error/mod.rs

@@ -0,0 +1,3 @@
+mod user;
+
+pub use user::UserError;

thoughts-backend/app/src/error/user.rs

@@ -0,0 +1,14 @@
+#[derive(Debug)]
+pub enum UserError {
+    NotFound,
+}
+
+impl std::fmt::Display for UserError {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        match self {
+            UserError::NotFound => write!(f, "User not found"),
+        }
+    }
+}
+
+impl std::error::Error for UserError {}