feat(ai): improve runtime capability reporting and context settings

Add explicit chat capability tracking, expose formatted runtime capabilities
in the info command, and support a max context size option for user AI settings.

Also update Ollama base URL resolution to use OLLAMA_ADDRESS and simplify
provider chat command execution.

src/model/ai-model-capabilities.ts

@@ -1,6 +1,7 @@
 import {AiCapabilityInfo} from "./ai-capability-info";
 
 export class AiModelCapabilities {
+    chat: AiCapabilityInfo | undefined;
     vision: AiCapabilityInfo | undefined;
     ocr: AiCapabilityInfo | undefined;
     thinking: AiCapabilityInfo | undefined;