feat: model registry and capabilities for multi-provider support (#2158)

* feat: Implement model registry and capabilities for multi-provider support

- Added ModelRegistry to manage available models and their capabilities.
- Introduced ModelProvider enum for different LLM providers.
- Created ModelCapabilities dataclass to define model features.
- Implemented methods to load models based on API keys and settings.
- Added utility functions for model management in model_utils.py.
- Updated settings.py to include provider-specific API keys.
- Refactored LLM classes (Anthropic, OpenAI, Google, etc.) to utilize new model registry.
- Enhanced utility functions to handle token limits and model validation.
- Improved code structure and logging for better maintainability.

* feat: Add model selection feature with API integration and UI component

* feat: Add model selection and default model functionality in agent management

* test: Update assertions and formatting in stream processing tests

* refactor(llm): Standardize model identifier to model_id

* fix tests

---------

Co-authored-by: Alex <a@tushynski.me>

application/api/user/models/routes.py

@@ -0,0 +1,25 @@
+from flask import current_app, jsonify, make_response
+from flask_restx import Namespace, Resource
+
+from application.core.model_settings import ModelRegistry
+
+models_ns = Namespace("models", description="Available models", path="/api")
+
+
+@models_ns.route("/models")
+class ModelsListResource(Resource):
+    def get(self):
+        """Get list of available models with their capabilities."""
+        try:
+            registry = ModelRegistry.get_instance()
+            models = registry.get_enabled_models()
+
+            response = {
+                "models": [model.to_dict() for model in models],
+                "default_model_id": registry.default_model_id,
+                "count": len(models),
+            }
+        except Exception as err:
+            current_app.logger.error(f"Error fetching models: {err}", exc_info=True)
+            return make_response(jsonify({"success": False}), 500)
+        return make_response(jsonify(response), 200)