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/openai-set-model.ts

@@ -0,0 +1,25 @@
+import {Command} from "../base/command";
+import {Requirements} from "../base/requirements";
+import {Requirement} from "../base/requirement";
+import {Message} from "typescript-telegram-bot-api";
+import {Environment} from "../common/environment";
+import {logError, replyToMessage} from "../util/utils";
+
+export class OpenAISetModel extends Command {
+    argsMode = "required" as const;
+
+    title = "/openAISetModel";
+    description = "Set OpenAI model";
+
+    requirements = Requirements.Build(Requirement.BOT_CREATOR);
+
+    async execute(msg: Message, match?: RegExpExecArray | null): Promise<void> {
+        const newModel = match?.[3];
+        Environment.setOpenAIModel(newModel || Environment.OPENAI_MODEL);
+
+        const text = newModel ? `Выбрана модель "${newModel}"`
+            : `Модель не задана. Будет использоваться стандартная модель "${Environment.OPENAI_MODEL}".`;
+
+        await replyToMessage({message: msg, text: text}).catch(logError);
+    }
+}