feat(openai): add chat streaming and model commands

- add /openai (/chatgpt) chat command using OpenAI Responses API (streaming + incremental edits)
- add /openAIListModels, /openAIGetModel, /openAISetModel
- introduce base Command class and migrate non-chat commands to it
- wire OpenAI client + env vars (OPENAI_API_KEY, OPENAI_MODEL)
- bump deps (@google/genai, systeminformation, @types/node) and add openai

src/commands/gemini-list-models.ts

@@ -1,11 +1,11 @@
-import {ChatCommand} from "../base/chat-command";
+import {Command} from "../base/command";
 import {Requirements} from "../base/requirements";
 import {Requirement} from "../base/requirement";
 import {Message} from "typescript-telegram-bot-api";
 import {googleAi} from "../index";
 import {logError, replyToMessage} from "../util/utils";
 
-export class GeminiListModels extends ChatCommand {
+export class GeminiListModels extends Command {
     title = "/geminiListModels";
     description = "List all Gemini models";