Refactor session ID handling and improve error management

- Introduced `SessionId` newtype for validated session identifiers, ensuring safety against path traversal attacks.
- Updated session repository methods to accept `SessionId` instead of raw strings, enhancing type safety.
- Removed redundant error handling in repository methods by leveraging the new `Error` type from `zesdex_utils`.
- Simplified atomic JSON write operations by eliminating unnecessary error conversions.
- Enhanced integer casting with a new `CastOr` trait for safer narrowing conversions.
- Removed deprecated error handling code and consolidated error types across the codebase.
- Updated HTTP handlers to utilize the new session ID validation, improving overall robustness.

crates/zesdex-iam/src/domain/repository.rs

@@ -11,6 +11,8 @@
 //! - [`OAuthRepository`] — persist/load OAuth tokens
 use std::path::Path;
 
+use zesdex_entities::domain::auth::SessionId;
+
 use crate::domain::error::RepositoryError;
 use crate::domain::oauth::OAuthToken;
 use crate::domain::session::Session;
@@ -21,13 +23,13 @@ pub trait SessionRepository {
     fn list_sessions(&self, base_dir: &Path) -> Result<Vec<Session>, RepositoryError>;
 
     /// Load a single session by id.
-    fn load_session(&self, base_dir: &Path, id: &str) -> Result<Session, RepositoryError>;
+    fn load_session(&self, base_dir: &Path, id: &SessionId) -> Result<Session, RepositoryError>;
 
     /// Save a session's metadata to disk.
     fn save_session(&self, base_dir: &Path, session: &Session) -> Result<(), RepositoryError>;
 
     /// Delete a session directory and all its contents.
-    fn delete_session(&self, base_dir: &Path, id: &str) -> Result<(), RepositoryError>;
+    fn delete_session(&self, base_dir: &Path, id: &SessionId) -> Result<(), RepositoryError>;
 }
 
 /// Repository for per-session PID-file advisory locks.