fix: real AP id tests, exact poster key check, exists port, list_movies fake

crates/domain/src/ports/images.rs

@@ -11,6 +11,8 @@ pub trait ObjectStorage: Send + Sync {
         key: &str,
     ) -> Result<futures::stream::BoxStream<'static, Result<bytes::Bytes, DomainError>>, DomainError>;
     async fn delete(&self, key: &str) -> Result<(), DomainError>;
+    /// Whether exactly `key` exists. Unlike `get`, no extension fallback.
+    async fn exists(&self, key: &str) -> Result<bool, DomainError>;
 }
 
 #[async_trait]