Add TTS proxy to fix CORS issues

- /api/tts proxies requests to Edge TTS and Kokoro
- Uses Docker container names for internal networking
- Removes URL config from settings (handled server-side)
- Fixes localStorage merge for new settings fields

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

src/app/api/tts/route.ts

@@ -0,0 +1,74 @@
+import { NextRequest, NextResponse } from "next/server";
+
+// POST /api/tts - Proxy TTS requests to avoid CORS issues
+export async function POST(request: NextRequest) {
+  try {
+    const body = await request.json();
+    const { engine, url, text, voice, speed } = body;
+
+    if (!text) {
+      return NextResponse.json({ error: "Text is required" }, { status: 400 });
+    }
+
+    let ttsUrl: string;
+    let ttsBody: Record<string, unknown>;
+
+    if (engine === "edge") {
+      // Use Docker container name for internal networking, fallback to provided URL
+      const edgeHost = process.env.EDGE_TTS_URL || url || "http://edge-tts:5050";
+      ttsUrl = `${edgeHost}/v1/audio/speech`;
+      ttsBody = {
+        model: "tts-1",
+        input: text,
+        voice: voice || "en-US-AvaNeural",
+        response_format: "mp3",
+        speed: speed || 1.0,
+      };
+    } else if (engine === "kokoro") {
+      // Use Docker container name for internal networking, fallback to provided URL
+      const kokoroHost = process.env.KOKORO_TTS_URL || url || "http://kokoro-tts:8880";
+      ttsUrl = `${kokoroHost}/v1/audio/speech`;
+      ttsBody = {
+        model: "kokoro",
+        input: text,
+        voice: voice || "af_bella",
+        response_format: "mp3",
+        speed: speed || 1.0,
+      };
+    } else {
+      return NextResponse.json({ error: "Invalid engine" }, { status: 400 });
+    }
+
+    const response = await fetch(ttsUrl, {
+      method: "POST",
+      headers: {
+        "Content-Type": "application/json",
+      },
+      body: JSON.stringify(ttsBody),
+    });
+
+    if (!response.ok) {
+      const errorText = await response.text();
+      console.error("TTS error:", response.status, errorText);
+      return NextResponse.json(
+        { error: `TTS service error: ${response.status}` },
+        { status: 502 }
+      );
+    }
+
+    const audioBuffer = await response.arrayBuffer();
+
+    return new NextResponse(audioBuffer, {
+      headers: {
+        "Content-Type": "audio/mpeg",
+        "Content-Length": audioBuffer.byteLength.toString(),
+      },
+    });
+  } catch (error) {
+    console.error("TTS proxy error:", error);
+    return NextResponse.json(
+      { error: error instanceof Error ? error.message : "TTS proxy failed" },
+      { status: 500 }
+    );
+  }
+}