Add Discord-native hybrid front-end for Jarvis (bot + bridge)

Transform isair/jarvis into a Discord-controlled voice assistant running on
the Ubuntu VNC desktop, keeping the mature ~39k-line Python brain intact.

- bot/ (Node + bun, discord.js): /자비스 slash commands (ephemeral),
  voice channel join + voice receive/playback, pluggable VNC screen broadcast
  (selfbot live / noVNC / screenshot)
- bridge/ (Python, Flask): wraps jarvis STT + run_reply_engine + Piper TTS
  behind a thin localhost HTTP API
- .env.example, scripts/ (start_bridge/start_bot/dev), README rewrite,
  docs/language-comparison.md and docs/vnc-xfce-setup.md

Language decision: hybrid (Python brain + Node/bun Discord layer) because
Discord blocks bot video; native screen broadcast only works via a Node
selfbot library.

bot/src/stream/index.ts

@@ -0,0 +1,51 @@
+/**
+ * Pluggable VNC screen-broadcast backends.
+ *
+ * Per the chosen design (option 1): the streaming method is swappable via
+ * STREAM_BACKEND in .env. The default is the real live "Go Live" stream via a
+ * selfbot account (only way to get a native Discord video broadcast), with safe
+ * fallbacks (noVNC link / periodic screenshots) available without code changes.
+ */
+import type { AppConfig } from "../config.ts";
+
+export interface StreamContext {
+  guildId: string;
+  voiceChannelId: string;
+  /** Post an image to the invoking text channel (used by the screenshot backend). */
+  postImage?: (png: Buffer, name: string) => Promise<void>;
+}
+
+export interface ScreenStreamer {
+  readonly kind: AppConfig["streamBackend"];
+  /** Start broadcasting. Returns a short user-facing status/link message. */
+  start(ctx: StreamContext): Promise<string>;
+  stop(): Promise<void>;
+  isActive(): boolean;
+}
+
+export async function createStreamer(config: AppConfig): Promise<ScreenStreamer> {
+  switch (config.streamBackend) {
+    case "selfbot": {
+      const { SelfbotStreamer } = await import("./selfbot.ts");
+      return new SelfbotStreamer(config);
+    }
+    case "novnc": {
+      const { NoVncStreamer } = await import("./novnc.ts");
+      return new NoVncStreamer(config);
+    }
+    case "screenshot": {
+      const { ScreenshotStreamer } = await import("./screenshot.ts");
+      return new ScreenshotStreamer(config);
+    }
+    case "none":
+    default:
+      return {
+        kind: "none",
+        async start() {
+          return "화면 송출이 비활성화되어 있습니다 (STREAM_BACKEND=none).";
+        },
+        async stop() {},
+        isActive: () => false,
+      };
+  }
+}