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/user.py

@@ -0,0 +1,66 @@
+from sqlalchemy import Column, Integer, String, Boolean, DateTime, ForeignKey, UniqueConstraint, func
+from sqlalchemy.orm import relationship
+import bcrypt as _bcrypt
+from ..database import Base
+
+
+class User(Base):
+    __tablename__ = "users"
+
+    id = Column(Integer, primary_key=True, index=True)
+    username = Column(String(100), unique=True, nullable=False, index=True)
+    password_hash = Column(String(200), nullable=False)
+    max_connections = Column(Integer, default=1, nullable=False)
+    expiry_date = Column(DateTime(timezone=True), nullable=True)
+    is_active = Column(Boolean, default=True, nullable=False)
+    is_priority = Column(Boolean, default=False, nullable=False)
+    created_at = Column(DateTime(timezone=True), server_default=func.now())
+
+    catalog_entries = relationship("UserCatalogEntry", back_populates="user", cascade="all, delete-orphan")
+    provider_preferences = relationship("UserProviderPreference", back_populates="user", cascade="all, delete-orphan", order_by="UserProviderPreference.priority")
+
+    def set_password(self, password: str) -> None:
+        hashed = _bcrypt.hashpw(password.encode(), _bcrypt.gensalt())
+        self.password_hash = hashed.decode()
+
+    def verify_password(self, password: str) -> bool:
+        return _bcrypt.checkpw(password.encode(), self.password_hash.encode())
+
+
+class UserCatalogEntry(Base):
+    __tablename__ = "user_catalog_entries"
+
+    id = Column(Integer, primary_key=True, index=True)
+    user_id = Column(Integer, ForeignKey("users.id", ondelete="CASCADE"), nullable=False)
+    category_id = Column(Integer, ForeignKey("categories.id", ondelete="CASCADE"), nullable=False)
+
+    user = relationship("User", back_populates="catalog_entries")
+    category = relationship("Category", back_populates="catalog_entries")
+
+
+class UserCustomCatalogEntry(Base):
+    __tablename__ = "user_custom_catalog_entries"
+
+    id = Column(Integer, primary_key=True, index=True)
+    user_id = Column(Integer, ForeignKey("users.id", ondelete="CASCADE"), nullable=False)
+    custom_category_id = Column(Integer, ForeignKey("custom_categories.id", ondelete="CASCADE"), nullable=False)
+
+    __table_args__ = (
+        UniqueConstraint("user_id", "custom_category_id", name="uq_user_custom_cat"),
+    )
+
+
+class UserProviderPreference(Base):
+    __tablename__ = "user_provider_preferences"
+
+    id = Column(Integer, primary_key=True, index=True)
+    user_id = Column(Integer, ForeignKey("users.id", ondelete="CASCADE"), nullable=False)
+    provider_account_id = Column(Integer, ForeignKey("provider_accounts.id", ondelete="CASCADE"), nullable=False)
+    priority = Column(Integer, default=0, nullable=False)
+
+    user = relationship("User", back_populates="provider_preferences")
+    provider_account = relationship("ProviderAccount")
+
+    __table_args__ = (
+        UniqueConstraint("user_id", "provider_account_id", name="uq_user_provider_pref"),
+    )