feat(server): refactor provider interface (#11665)

fix AI-4
fix AI-18

better provider/model choose to allow fallback to similar models (e.g., self-hosted) when the provider is not fully configured
split functions of different output types

packages/backend/server/src/plugins/copilot/resolver.ts

@@ -228,9 +228,6 @@ registerEnumType(AiPromptRole, {
 @InputType('CopilotPromptConfigInput')
 @ObjectType()
 class CopilotPromptConfigType {
-  @Field(() => Boolean, { nullable: true })
-  jsonMode!: boolean | null;
-
   @Field(() => Float, { nullable: true })
   frequencyPenalty!: number | null;