Model capabilities 734 (#842)

internal/config,server: implement model capabilities

- define the capabilities of a model using a simple config block on the
model
- v1/models renders out capabilities to be compatible with openrouter,
huggingface chat, and mistral formats for broader compatibility
- add support for capabilities in UI

Fixes #734

ui-svelte/src/components/playground/ImageInterface.svelte

@@ -193,7 +193,7 @@
 <div class="flex flex-col h-full">
   <!-- Model selector and mode toggle -->
   <div class="shrink-0 flex flex-wrap gap-2 mb-4">
-    <ModelSelector bind:value={$selectedModelStore} placeholder="Select an image model..." disabled={isGenerating} />
+    <ModelSelector bind:value={$selectedModelStore} placeholder="Select an image model..." disabled={isGenerating} capabilities={["image_generation", "image_to_image"]} matchAny={true} />
 
     <select
       class="px-3 py-2 rounded border border-gray-200 dark:border-white/10 bg-surface focus:outline-none focus:ring-2 focus:ring-primary"