Restructure into asr/tts packages and add TTS tab skeleton

Split the single ASR gateway into app/main.py (entrypoint) + app/core
(shared env helpers) + app/asr (all existing ASR logic, unchanged
behavior) + app/tts (placeholder router/config, no engine yet), so a
real TTS backend can be dropped in later without reshuffling ASR code.
API moved under /asr/* and /tts/* prefixes; UI gained a top-level
ASR/TTS tab switcher built on a reusable nested .tab-group mechanism,
with JS split into common.js/asr.js/tts.js.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

app/main.py

@@ -0,0 +1,48 @@
+from __future__ import annotations
+
+from pathlib import Path
+from typing import Any, Dict
+
+from fastapi import FastAPI
+from fastapi.middleware.cors import CORSMiddleware
+from fastapi.responses import FileResponse, HTMLResponse, JSONResponse
+from fastapi.staticfiles import StaticFiles
+
+from asr.config import ensure_runtime_dirs
+from asr.router import router as asr_router
+from tts.router import router as tts_router
+
+app = FastAPI(title="ASR/TTS Gateway", docs_url="/docs", redoc_url="/redoc")
+app.add_middleware(
+    CORSMiddleware,
+    allow_origins=["*"],
+    allow_credentials=True,
+    allow_methods=["*"],
+    allow_headers=["*"],
+)
+
+UI_DIR = Path("/app/ui")
+
+app.include_router(asr_router, prefix="/asr", tags=["asr"])
+app.include_router(tts_router, prefix="/tts", tags=["tts"])
+
+
+@app.on_event("startup")
+def startup() -> None:
+    ensure_runtime_dirs()
+    if UI_DIR.exists():
+        app.mount("/ui", StaticFiles(directory=str(UI_DIR), html=True), name="ui")
+        app.mount("/assets", StaticFiles(directory=str(UI_DIR / "assets")), name="assets")
+
+
+@app.get("/health")
+def health() -> Dict[str, Any]:
+    return {"status": "ok", "ui_installed": UI_DIR.exists(), "api": "/docs"}
+
+
+@app.get("/", response_class=HTMLResponse)
+def root() -> Any:
+    index = UI_DIR / "index.html"
+    if index.exists():
+        return FileResponse(index)
+    return JSONResponse({"status": "ok", "message": "UI not installed", "api": "/docs"})