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>

frontend/src/agents/agentPreviewSlice.ts

@@ -52,6 +52,10 @@ export const fetchPreviewAnswer = createAsyncThunk<
     }
 
     if (state.preference) {
+      const modelId =
+        state.preference.selectedAgent?.default_model_id ||
+        state.preference.selectedModel?.id;
+
       if (API_STREAMING) {
         await handleFetchAnswerSteaming(
           question,
@@ -120,22 +124,23 @@ export const fetchPreviewAnswer = createAsyncThunk<
           indx,
           state.preference.selectedAgent?.id,
           attachmentIds,
-          false, // Don't save preview conversations
+          false,
+          modelId,
         );
       } else {
-        // Non-streaming implementation
         const answer = await handleFetchAnswer(
           question,
           signal,
           state.preference.token,
           state.preference.selectedDocs,
-          null, // No conversation ID for previews
+          null,
           state.preference.prompt.id,
           state.preference.chunks,
           state.preference.token_limit,
           state.preference.selectedAgent?.id,
           attachmentIds,
-          false, // Don't save preview conversations
+          false,
+          modelId,
         );
 
         if (answer) {