Mejoras de estabilidad de stream IPTV y nuevo registro de fallos

- restream.py: eliminar -reconnect_streamed de ffmpeg para evitar rebobinados
  al reconectar (el proveedor re-enviaba desde keyframe anterior causando PTS
  backward). El loop de Python gestiona las reconexiones con conexión fresca.
- restream.py: eliminar _drain_queue del loop de reconexión para que el buffer
  de la cola cubra el tiempo de reconexión sin pantalla negra en el player.
- restream.py: añadir buffer_server_bytes/secs/capacity a stats() y método
  _log_stream_event() para persistir eventos de caída y recuperación en BD.
- models/stream_event.py: nuevo modelo StreamEvent para registro de fallos.
- database.py: registrar StreamEvent en init_db.
- api/admin/logs.py: nuevos endpoints GET/DELETE /logs/events.
- Dashboard.tsx: mostrar reserva de buffer del servidor (capacidad + estado).
- Logs.tsx: añadir pestaña "Fallos de stream" con tabla de eventos persistidos.

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

backend/models/provider.py

@@ -0,0 +1,41 @@
+from sqlalchemy import Column, Integer, String, Boolean, DateTime, Text, ForeignKey, func
+from sqlalchemy.orm import relationship
+from ..database import Base
+
+
+class ProviderAccount(Base):
+    __tablename__ = "provider_accounts"
+
+    id = Column(Integer, primary_key=True, index=True)
+    name = Column(String(100), nullable=False)
+    base_url = Column(String(500), nullable=False)
+    username = Column(String(200), nullable=False)
+    password = Column(String(200), nullable=False)
+    max_connections = Column(Integer, default=1, nullable=False)
+    is_active = Column(Boolean, default=True, nullable=False)
+    last_sync_at = Column(DateTime(timezone=True), nullable=True)
+    expiry_date = Column(DateTime(timezone=True), nullable=True)
+    # 0 = disabled; 6/12/24 = sync every N hours automatically
+    auto_sync_hours = Column(Integer, default=0, nullable=False)
+    # JSON: {"live": ["cat_id", ...], "movie": [...], "series": [...]}
+    last_sync_categories = Column(Text, nullable=True)
+    created_at = Column(DateTime(timezone=True), server_default=func.now())
+
+    channel_maps = relationship("ChannelProviderMap", back_populates="provider_account", cascade="all, delete-orphan")
+    extra_urls = relationship("ProviderUrl", back_populates="provider_account", cascade="all, delete-orphan", order_by="ProviderUrl.priority")
+
+
+class ProviderUrl(Base):
+    __tablename__ = "provider_urls"
+
+    id = Column(Integer, primary_key=True, index=True)
+    provider_account_id = Column(Integer, ForeignKey("provider_accounts.id", ondelete="CASCADE"), nullable=False, index=True)
+    url = Column(String(500), nullable=False)
+    priority = Column(Integer, default=0, nullable=False)  # 0=primary, higher=lower priority
+    is_active = Column(Boolean, default=True, nullable=False)
+    status = Column(String(20), default="unknown", nullable=False)  # unknown|ok|error|timeout
+    response_ms = Column(Integer, nullable=True)
+    last_checked_at = Column(DateTime(timezone=True), nullable=True)
+    created_at = Column(DateTime(timezone=True), server_default=func.now())
+
+    provider_account = relationship("ProviderAccount", back_populates="extra_urls")