domain crate code quality cleanup

strip all comments, extract tests to tests/ dirs,
remove #[allow(clippy::...)], extract magic numbers to
constants, refactor schedule engine private methods to
use param structs, add Default impls, clippy.toml for
persistence constructors

crates/domain/src/ports/transcode.rs

@@ -1,18 +1,10 @@
-//! Transcode settings port.
-//!
-//! Persists FFmpeg transcoding configuration (cleanup TTL, etc.).
-//! Small enough to keep as a single trait.
-
 use async_trait::async_trait;
 
 use crate::errors::DomainResult;
 
-/// Port for transcode settings persistence.
 #[async_trait]
 pub trait TranscodeSettingsRepository: Send + Sync {
-    /// Load the persisted cleanup TTL. Returns `None` if no row exists yet.
     async fn load_cleanup_ttl(&self) -> DomainResult<Option<u32>>;
 
-    /// Persist the cleanup TTL (upsert -- always row id=1).
     async fn save_cleanup_ttl(&self, hours: u32) -> DomainResult<()>;
 }