### FEAT: Add Vega Char Visualizer Renderer
Feature required in https://github.com/open-webui/open-webui/discussions/18022
Added npm vega lib to package.json
Added function for visualization renderer to src/libs/utils/index.ts
Added logic to src/lib/components/chat/Messages/CodeBlock.svelte
The treatment is similar as for mermaid diagrams.
Reference: https://vega.github.io/vega/
This commit introduces the necessary logic and UI controls to allow users to switch the Flow component layout between vertical and horizontal orientations.
* **`Flow.svelte` Refactoring:**
* Updates logic for calculating level offsets and node positions to consistently respect the current flow orientation.
* Adds a control panel using `<Controls>` and `<SwitchButton>` components.
* Provides user interface elements to easily switch the flow layout between horizontal and vertical orientations.
This refactors the model import functionality to improve performance and user experience by centralizing the logic on the backend.
Previously, the frontend would parse an imported JSON file and send an individual API request for each model, which was slow and inefficient.
This change introduces a new backend endpoint, `/api/v1/models/import`, that accepts a list of model objects. The frontend now reads the selected JSON file, parses it, and sends the entire payload to the backend in a single request. The backend then processes this list, creating or updating models as necessary.
This commit also includes the following fixes:
- Handles cases where the imported JSON contains models without `meta` or `params` fields by providing default empty values.
This moves the JSON model import functionality to the backend. Instead of the frontend parsing the JSON file and sending multiple requests, it now uploads the file to a new endpoint (/api/v1/models/import), which processes the file and imports the models. This improves efficiency and provides better user feedback.
