Rebuild frontend with Tailwind CSS + fix Python 3.14 compatibility

- Upgrade SQLAlchemy 2.0.27→2.0.45, google-genai SDK for Python 3.14
- Replace google-generativeai with google-genai in narrative_service.py
- Fix HTTPException handling in main.py (was wrapping as 500)
- Rebuild all frontend components with Tailwind CSS v3:
  - Dashboard, NarrativeSection, StatsGrid, VibeRadar, HeatMap, TopRotation
  - Custom color palette (background-dark, card-dark, accent-neon, etc.)
  - Add glass-panel, holographic-badge CSS effects
- Docker improvements:
  - Combined backend container (API + worker in entrypoint.sh)
  - DATABASE_URL configurable via env var
  - CI workflow builds both backend and frontend images
- Update README with clearer docker-compose instructions

backend/app/database.py

@@ -1,11 +1,14 @@
+import os
 from sqlalchemy import create_engine
 from sqlalchemy.orm import sessionmaker, declarative_base
 
-SQLALCHEMY_DATABASE_URL = "sqlite:///./music.db"
+SQLALCHEMY_DATABASE_URL = os.getenv("DATABASE_URL", "sqlite:///./music.db")
 
-engine = create_engine(
-    SQLALCHEMY_DATABASE_URL, connect_args={"check_same_thread": False}
-)
+connect_args = {}
+if SQLALCHEMY_DATABASE_URL.startswith("sqlite"):
+    connect_args["check_same_thread"] = False
+
+engine = create_engine(SQLALCHEMY_DATABASE_URL, connect_args=connect_args)
 SessionLocal = sessionmaker(autocommit=False, autoflush=False, bind=engine)
 
 Base = declarative_base()