Fix Anthropic model metadata (#9825)

Address #9785 

The model's metadata is used to determine whether it's allowed for
selection in the chat input. Anthropic doesn't return any data on model
capabilities so we've been hard-coding them. This is a regression when
building the model metadata after fetching the model listing where it
omits setting the capabilities.

Agent and Edit modes need the model to support `agentMode` and
`toolCalling` to display in the list.

### Release Notes

#### New Features

- N/A

#### Bug Fixes

- N/A


### QA Notes
This only affected Anthropic. Bedrock and the other Vercel backed
providers use the proper values.

Author: timtmok

extensions/positron-assistant/src/anthropic.ts

@@ -333,7 +333,7 @@ export class AnthropicLanguageModel implements positron.ai.LanguageModelChatProv
 					version: model.created_at,
 					maxInputTokens: maxInputTokens,
 					maxOutputTokens: maxOutputTokens,
-					capabilities: {},
+					capabilities: this.capabilities,
 					isDefault: isFirst,
 					isUserSelectable: true,
 				});