refactor(core): remove provider module, migrate to LLMProvider, add client mode handling, improve serialization error handling, update workspace edition, and clean up conditionals and imports

docs/provider-implementation.md

@@ -36,7 +36,7 @@ In your new crate's `lib.rs`, you will define a struct for your provider and imp
 ```rust
 use async_trait::async_trait;
 use owlen_core::model::Model;
-use owlen_core::provider::Provider;
+use owlen_core::Provider;
 use owlen_core::session::Session;
 
 pub struct MyProvider;