Add session persistence and browser functionality

- Implement `StorageManager` for saving, loading, and managing sessions.
- Introduce platform-specific session directories for persistence.
- Add session browser UI for listing, loading, and deleting saved sessions.
- Enable AI-generated descriptions for session summaries.
- Update configurations to support storage settings and description generation.
- Extend README and tests to document and validate new functionality.

crates/owlen-core/src/conversation.rs

@@ -1,7 +1,9 @@
+use crate::storage::StorageManager;
 use crate::types::{Conversation, Message};
 use crate::Result;
 use serde_json::{Number, Value};
 use std::collections::{HashMap, VecDeque};
+use std::path::{Path, PathBuf};
 use std::time::{Duration, Instant};
 use uuid::Uuid;
 
@@ -47,8 +49,8 @@ impl ConversationManager {
         &self.active
     }
 
-    /// Mutable access to the active conversation (auto refreshing indexes afterwards)
-    fn active_mut(&mut self) -> &mut Conversation {
+    /// Public mutable access to the active conversation
+    pub fn active_mut(&mut self) -> &mut Conversation {
         &mut self.active
     }
 
@@ -264,6 +266,33 @@ impl ConversationManager {
     fn stream_reset(&mut self) {
         self.streaming.clear();
     }
+
+    /// Save the active conversation to disk
+    pub fn save_active(&self, storage: &StorageManager, name: Option<String>) -> Result<PathBuf> {
+        storage.save_conversation(&self.active, name)
+    }
+
+    /// Save the active conversation to disk with a description
+    pub fn save_active_with_description(
+        &self,
+        storage: &StorageManager,
+        name: Option<String>,
+        description: Option<String>
+    ) -> Result<PathBuf> {
+        storage.save_conversation_with_description(&self.active, name, description)
+    }
+
+    /// Load a conversation from disk and make it active
+    pub fn load_from_disk(&mut self, storage: &StorageManager, path: impl AsRef<Path>) -> Result<()> {
+        let conversation = storage.load_conversation(path)?;
+        self.load(conversation);
+        Ok(())
+    }
+
+    /// List all saved sessions
+    pub fn list_saved_sessions(storage: &StorageManager) -> Result<Vec<crate::storage::SessionMeta>> {
+        storage.list_sessions()
+    }
 }
 
 impl StreamingMetadata {