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/asr/config.py

@@ -0,0 +1,40 @@
+from __future__ import annotations
+
+from pathlib import Path
+from typing import Optional
+
+from core.config import env_str
+
+ASR_BASE_DIR = Path(env_str("ASR_BASE_DIR", "/srv/asr"))
+MODEL_CACHE = Path(env_str("WHISPER_CACHE_DIR", str(ASR_BASE_DIR / "models-cache")))
+UPLOAD_DIR = ASR_BASE_DIR / "uploads"
+RESULT_DIR = ASR_BASE_DIR / "results"
+CUSTOM_MODEL_DIR = ASR_BASE_DIR / "custom-models"
+
+DEVICE = env_str("ASR_DEVICE", "cuda")
+COMPUTE_TYPE = env_str("ASR_COMPUTE_TYPE", "float16")
+DEFAULT_BACKEND = env_str("DEFAULT_BACKEND", "faster-whisper")
+DEFAULT_MODEL = env_str("DEFAULT_MODEL", "large-v3")
+DEFAULT_LANGUAGE = env_str("DEFAULT_LANGUAGE", "ko")
+
+FASTER_WHISPER_URL = env_str("FASTER_WHISPER_URL", "http://127.0.0.1:8001")
+QWEN3_URL = env_str("QWEN3_URL", "http://127.0.0.1:8004")
+
+PYANNOTE_HF_TOKEN = env_str("PYANNOTE_HF_TOKEN", "")
+
+
+def ensure_runtime_dirs() -> None:
+    for p in [ASR_BASE_DIR, MODEL_CACHE, UPLOAD_DIR, RESULT_DIR, CUSTOM_MODEL_DIR]:
+        p.mkdir(parents=True, exist_ok=True)
+
+
+def resolve_custom_model_path(custom_model_path: Optional[str]) -> Optional[str]:
+    if not custom_model_path:
+        return None
+    raw = custom_model_path.strip()
+    if not raw:
+        return None
+    candidate = Path(raw)
+    if candidate.is_absolute():
+        return str(candidate)
+    return str((CUSTOM_MODEL_DIR / candidate).resolve())