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

config.example.yaml

@@ -312,6 +312,37 @@ models:
       tlsHandshake: 10
       idleConn: 90
 
+    # capabilities: defines what the model accepts for input, output and other metadata
+    # - optional; omitted or all-zero means no capabilities
+    # - used in v1/models to inform clients what the model can do
+    capabilities:
+      # in: list of modalities understood by the model
+      # - default: []
+      # - valid: text, audio, image
+      in:
+        - text
+        - audio
+        - image
+      # out: list of modalities generated by the model
+      # - default: []
+      # - valid: text, audio, image
+      out:
+        - text
+        - audio
+        - image
+      # tools: the model supports function calling
+      # - default: false
+      tools: true
+
+      # reranker: the model supports the /v1/rerank endpoint
+      # - default: false
+      reranker: false
+
+      # context: the maximum token context length supported
+      # - default: 0
+      # - must be an integer > 0
+      context: 32000
+
   # Unlisted model example:
   "qwen-unlisted":
     # unlisted: boolean, true or false