refactor(ollama)!: remove Ollama provider crate and implementation

Deletes the `owlen-ollama` Cargo.toml and source files, fully removing the Ollama provider from the workspace. This aligns the project with the MCP‑only architecture and eliminates direct provider dependencies.

crates/owlen-core/src/credentials.rs

@@ -10,6 +10,8 @@ pub struct ApiCredentials {
     pub endpoint: String,
 }
 
+pub const OLLAMA_CLOUD_CREDENTIAL_ID: &str = "provider_ollama_cloud";
+
 pub struct CredentialManager {
     storage: Arc<StorageManager>,
     master_key: Arc<Vec<u8>>,