feat(agent): model sync improvements - deduplication and offline status

- Add Offline status to ModelStatus enum
- Sync marks all models offline first, then activates found ones
- Deduplicate by model name (ignoring provider)
- Deactivate orphaned models (offline -> deprecated)
- Add models_offline and models_deactivated to SyncModelsResponse
- Add deduplicate_existing_models() for cleanup
- Rename upsert_model to upsert_model_by_name

libs/models/agents/mod.rs

@@ -67,12 +67,15 @@ impl std::str::FromStr for ModelCapability {
     }
 }
 
-/// Model or model-version availability status. Stored as `"active"` or
-/// `"deprecated"`.
+/// Model or model-version availability status.
 #[derive(Clone, Debug, PartialEq, Eq, Serialize, Deserialize)]
 pub enum ModelStatus {
+    /// Model is available and can be used.
     Active,
+    /// Model is no longer available from the provider.
     Deprecated,
+    /// Model was not found in the last upstream sync (offline).
+    Offline,
 }
 
 impl std::fmt::Display for ModelStatus {
@@ -80,6 +83,7 @@ impl std::fmt::Display for ModelStatus {
         match self {
             ModelStatus::Active => write!(f, "active"),
             ModelStatus::Deprecated => write!(f, "deprecated"),
+            ModelStatus::Offline => write!(f, "offline"),
         }
     }
 }
@@ -90,6 +94,7 @@ impl std::str::FromStr for ModelStatus {
         match s {
             "active" => Ok(ModelStatus::Active),
             "deprecated" => Ok(ModelStatus::Deprecated),
+            "offline" => Ok(ModelStatus::Offline),
             _ => Err("unknown model status"),
         }
     }