[ci skip] f1-stream: add extractor framework with demo streams (Phase 3)

- BaseExtractor ABC with health_check method
- ExtractorRegistry with concurrent fan-out extraction
- ExtractionService with in-memory cache and background polling
- DemoExtractor with 3 public HLS test streams
- Adaptive polling: 5min during live sessions, 30min otherwise
- GET /streams, GET /extractors, POST /extract endpoints

stacks/f1-stream/files/backend/extractors/models.py

@@ -0,0 +1,29 @@
+"""Data models for the stream extraction framework."""
+
+from dataclasses import dataclass, field
+from datetime import datetime, timezone
+
+
+@dataclass
+class ExtractedStream:
+    """Represents a single stream URL discovered by an extractor."""
+
+    url: str  # The HLS/m3u8 URL
+    site_key: str  # Which extractor found it
+    site_name: str  # Human-readable name
+    quality: str = ""  # e.g., "720p", "1080p", or empty
+    title: str = ""  # e.g., "F1 Race Live"
+    extracted_at: str = field(default_factory=lambda: datetime.now(timezone.utc).isoformat())
+    is_live: bool = False  # Whether it passed health check
+
+    def to_dict(self) -> dict:
+        """Serialize to a plain dictionary for JSON responses."""
+        return {
+            "url": self.url,
+            "site_key": self.site_key,
+            "site_name": self.site_name,
+            "quality": self.quality,
+            "title": self.title,
+            "extracted_at": self.extracted_at,
+            "is_live": self.is_live,
+        }