refactor(core): normalize core service naming

Standardize core service module and export names to reduce naming ambiguity and make imports predictable across runtime, tests, scripts, and docs.

src/core/services/subtitle-ws.ts

@@ -0,0 +1,60 @@
+import * as fs from "fs";
+import * as os from "os";
+import * as path from "path";
+import WebSocket from "ws";
+import { createLogger } from "../../logger";
+
+const logger = createLogger("main:subtitle-ws");
+
+export function hasMpvWebsocketPlugin(): boolean {
+  const mpvWebsocketPath = path.join(
+    os.homedir(),
+    ".config",
+    "mpv",
+    "mpv_websocket",
+  );
+  return fs.existsSync(mpvWebsocketPath);
+}
+
+export class SubtitleWebSocket {
+  private server: WebSocket.Server | null = null;
+
+  public isRunning(): boolean {
+    return this.server !== null;
+  }
+
+  public start(port: number, getCurrentSubtitleText: () => string): void {
+    this.server = new WebSocket.Server({ port, host: "127.0.0.1" });
+
+    this.server.on("connection", (ws: WebSocket) => {
+      logger.info("WebSocket client connected");
+      const currentText = getCurrentSubtitleText();
+      if (currentText) {
+        ws.send(JSON.stringify({ sentence: currentText }));
+      }
+    });
+
+    this.server.on("error", (err: Error) => {
+      logger.error("WebSocket server error:", err.message);
+    });
+
+    logger.info(`Subtitle WebSocket server running on ws://127.0.0.1:${port}`);
+  }
+
+  public broadcast(text: string): void {
+    if (!this.server) return;
+    const message = JSON.stringify({ sentence: text });
+    for (const client of this.server.clients) {
+      if (client.readyState === WebSocket.OPEN) {
+        client.send(message);
+      }
+    }
+  }
+
+  public stop(): void {
+    if (this.server) {
+      this.server.close();
+      this.server = null;
+    }
+  }
+}