Merge feature/btc-history-chart: BTC candlestick chart with local OHLC storage

Resolves conflicts: combined admin + candles routers in main.py,
fixed docker-compose port to 3001:3001, restored admin styles in Dashboard.

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

btc-portfolio/backend/app/models.py

@@ -25,3 +25,14 @@ class Purchase(Base):
     user_id = Column(Integer, ForeignKey("users.id"), nullable=False)
 
     owner = relationship("User", back_populates="purchases")
+
+
+class OHLCCandle(Base):
+    __tablename__ = "ohlc_candles"
+
+    id    = Column(Integer, primary_key=True, index=True)
+    date  = Column(String, unique=True, index=True, nullable=False)  # "YYYY-MM-DD" UTC
+    open  = Column(Float, nullable=False)
+    high  = Column(Float, nullable=False)
+    low   = Column(Float, nullable=False)
+    close = Column(Float, nullable=False)