feat(signal_v2): foundation — config + state + requirements

- signal_v2/config.py: Settings dataclass loading web-ai/.env explicitly
- signal_v2/state.py: PollState dataclass + module-level singleton
- requirements.txt: httpx / fastapi / uvicorn / pytest-asyncio / respx
- .gitignore: signal_v2/data/*.db (WAL/SHM)
- empty tests/ marker

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

signal_v2/config.py

@@ -0,0 +1,28 @@
+"""Signal V2 환경변수 로딩."""
+import os
+from dataclasses import dataclass, field
+from pathlib import Path
+
+from dotenv import load_dotenv
+
+# web-ai/.env 명시 로드 (signal_v2/config.py 의 parent.parent = web-ai/)
+load_dotenv(Path(__file__).parent.parent / ".env")
+
+
+@dataclass(frozen=True)
+class Settings:
+    stock_api_url: str = field(
+        default_factory=lambda: os.getenv("STOCK_API_URL", "").rstrip("/")
+    )
+    webai_api_key: str = field(
+        default_factory=lambda: os.getenv("WEBAI_API_KEY", "").strip()
+    )
+    port: int = field(default_factory=lambda: int(os.getenv("SIGNAL_V2_PORT", "8001")))
+    db_path: Path = field(
+        default_factory=lambda: Path(__file__).parent / "data" / "signal_v2.db"
+    )
+
+
+def get_settings() -> Settings:
+    """매 호출 시 신선한 Settings (테스트 monkeypatch 호환)."""
+    return Settings()