feat: full clean architecture refactor — domain → application → infrastructure → presentation

- Restructure from Modular MVC to Clean Architecture with 4 strict layers
- Domain: entities (anime/komik/proxy), Repository traits, typed errors
- Application: use case classes with proper error propagation
- Infrastructure: repository impls, parsers, Redis cache, HTTP/scraping, browser
- Presentation: Axum handlers, DTOs, AppState, router, AppError+IntoResponse
- Migrate all parsers (otakudesu, alqanime, komik) to native infra implementations
- Replace once_cell::sync::Lazy/OnceCell with std::sync::LazyLock/OnceLock
- Remove 150+ old files in modules/ and shared/ directories
- Remove once_cell from Cargo.toml dependencies
- Fix test/debug binaries to use new import paths
- Zero new clippy warnings

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/domain/error.rs

@@ -0,0 +1,55 @@
+//! Domain-level error types.
+//!
+//! These are framework-agnostic errors that can be mapped to HTTP errors
+//! at the presentation layer. Domain and application layers only use these.
+
+use thiserror::Error;
+
+/// Errors originating from repository operations (DB, HTTP, etc.)
+#[derive(Error, Debug)]
+pub enum RepositoryError {
+    #[error("Not found")]
+    NotFound,
+    #[error("Conflict: {0}")]
+    Conflict(String),
+    #[error("Database error: {0}")]
+    Database(String),
+    #[error("Network error: {0}")]
+    Network(String),
+}
+
+/// Errors originating from scraping/parsing operations
+#[derive(Error, Debug)]
+pub enum ScrapingError {
+    #[error("HTTP error: {0}")]
+    Http(String),
+    #[error("Parse error: {0}")]
+    Parse(String),
+    #[error("Empty response")]
+    EmptyResponse,
+}
+
+/// Generic domain error
+#[derive(Error, Debug)]
+pub enum DomainError {
+    #[error("Not found: {0}")]
+    NotFound(String),
+    #[error("Validation error: {0}")]
+    Validation(String),
+    #[error("Repository error: {0}")]
+    Repository(#[from] RepositoryError),
+    #[error("Scraping error: {0}")]
+    Scraping(#[from] ScrapingError),
+}
+
+impl From<String> for RepositoryError {
+    fn from(s: String) -> Self {
+        RepositoryError::Database(s)
+    }
+}
+
+impl From<&str> for RepositoryError {
+    fn from(s: &str) -> Self {
+        RepositoryError::Database(s.to_string())
+    }
+}