feat: initialize k-tv-frontend with Next.js and Tailwind CSS

- Added package.json with dependencies and scripts for development, build, and linting.
- Created postcss.config.mjs for Tailwind CSS integration.
- Added SVG assets for UI components including file, globe, next, vercel, and window icons.
- Configured TypeScript with tsconfig.json for strict type checking and module resolution.

k-tv-backend/domain/src/errors.rs

@@ -0,0 +1,92 @@
+//! Domain errors for K-Notes
+//!
+//! Uses `thiserror` for ergonomic error definitions.
+//! These errors represent domain-level failures and will be mapped
+//! to HTTP status codes in the API layer.
+
+use thiserror::Error;
+use uuid::Uuid;
+
+/// Domain-level errors for K-TV operations
+#[derive(Debug, Error)]
+#[non_exhaustive]
+pub enum DomainError {
+    /// The requested user was not found
+    #[error("User not found: {0}")]
+    UserNotFound(Uuid),
+
+    /// User with this email/subject already exists
+    #[error("User already exists: {0}")]
+    UserAlreadyExists(String),
+
+    /// The requested channel was not found
+    #[error("Channel not found: {0}")]
+    ChannelNotFound(Uuid),
+
+    /// No generated schedule exists and is active for the given channel and time
+    #[error("No active schedule for channel: {0}")]
+    NoActiveSchedule(Uuid),
+
+    /// A validation error occurred
+    #[error("Validation error: {0}")]
+    ValidationError(String),
+
+    /// A timezone string could not be parsed
+    #[error("Invalid timezone: {0}")]
+    TimezoneError(String),
+
+    /// User is not authenticated (maps to HTTP 401)
+    #[error("Unauthenticated: {0}")]
+    Unauthenticated(String),
+
+    /// User is not allowed to perform this action (maps to HTTP 403)
+    #[error("Forbidden: {0}")]
+    Forbidden(String),
+
+    /// A repository/infrastructure error occurred
+    #[error("Repository error: {0}")]
+    RepositoryError(String),
+
+    /// An infrastructure adapter error occurred
+    #[error("Infrastructure error: {0}")]
+    InfrastructureError(String),
+}
+
+impl DomainError {
+    /// Create a validation error
+    pub fn validation(message: impl Into<String>) -> Self {
+        Self::ValidationError(message.into())
+    }
+
+    /// Create an unauthenticated error (not logged in → 401)
+    pub fn unauthenticated(message: impl Into<String>) -> Self {
+        Self::Unauthenticated(message.into())
+    }
+
+    /// Create a forbidden error (not allowed → 403)
+    pub fn forbidden(message: impl Into<String>) -> Self {
+        Self::Forbidden(message.into())
+    }
+
+    /// Check if this error indicates a "not found" condition
+    pub fn is_not_found(&self) -> bool {
+        matches!(
+            self,
+            DomainError::UserNotFound(_) | DomainError::ChannelNotFound(_)
+        )
+    }
+
+    /// Check if this error indicates a conflict (already exists)
+    pub fn is_conflict(&self) -> bool {
+        matches!(self, DomainError::UserAlreadyExists(_))
+    }
+}
+
+impl From<crate::value_objects::ValidationError> for DomainError {
+    fn from(error: crate::value_objects::ValidationError) -> Self {
+        DomainError::ValidationError(error.to_string())
+    }
+}
+
+/// Result type alias for domain operations
+pub type DomainResult<T> = Result<T, DomainError>;