feat(signal_v2): pull_worker + FastAPI app + 2 integration tests

poll_loop: asyncio.gather parallel fetch of 3 endpoints (portfolio,
news_sentiment, screener_preview) + state update. main.py: FastAPI
lifespan creates StockClient/SignalDedup/shutdown.Event then spawns
poll_loop as background task. GET /health reports status, last poll
times, cache size.

Signal V2 test suite: 19/19 PASS.

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

signal_v2/main.py

@@ -0,0 +1,70 @@
+"""FastAPI app — Signal V2 Pull Worker."""
+from __future__ import annotations
+import asyncio
+import logging
+from contextlib import asynccontextmanager
+
+from fastapi import FastAPI
+
+from signal_v2 import state as state_mod
+from signal_v2.config import get_settings
+from signal_v2.pull_worker import poll_loop
+from signal_v2.rate_limit import SignalDedup
+from signal_v2.stock_client import StockClient
+
+logger = logging.getLogger(__name__)
+
+
+class AppContext:
+    client: StockClient | None = None
+    dedup: SignalDedup | None = None
+    shutdown: asyncio.Event | None = None
+    poll_task: asyncio.Task | None = None
+
+
+_ctx = AppContext()
+
+
+@asynccontextmanager
+async def lifespan(app: FastAPI):
+    settings = get_settings()
+    if not settings.webai_api_key:
+        logger.warning(
+            "WEBAI_API_KEY not configured — stock API calls will fail with 401"
+        )
+
+    _ctx.client = StockClient(settings.stock_api_url, settings.webai_api_key)
+    _ctx.dedup = SignalDedup(settings.db_path)
+    _ctx.shutdown = asyncio.Event()
+    _ctx.poll_task = asyncio.create_task(
+        poll_loop(_ctx.client, state_mod.state, _ctx.shutdown)
+    )
+
+    yield
+
+    # Shutdown
+    if _ctx.shutdown is not None:
+        _ctx.shutdown.set()
+    if _ctx.poll_task is not None:
+        try:
+            await asyncio.wait_for(_ctx.poll_task, timeout=5.0)
+        except asyncio.TimeoutError:
+            _ctx.poll_task.cancel()
+    if _ctx.client is not None:
+        await _ctx.client.close()
+
+
+app = FastAPI(
+    title="Signal V2 Pull Worker", version="0.1.0", lifespan=lifespan
+)
+
+
+@app.get("/health")
+async def health():
+    settings = get_settings()
+    return {
+        "status": "online",
+        "stock_api_url": settings.stock_api_url,
+        "last_poll": state_mod.state.last_updated,
+        "cache_size": len(_ctx.client._cache) if _ctx.client is not None else 0,
+    }