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/entrypoint.sh

@@ -0,0 +1,17 @@
+#!/bin/bash
+set -e
+
+echo "=== MusicAnalyser Backend Starting ==="
+
+# Run Alembic migrations
+echo "Running database migrations..."
+alembic upgrade head
+
+# Start the worker in background (polls Spotify every 60s)
+echo "Starting Spotify ingestion worker..."
+python run_worker.py &
+WORKER_PID=$!
+
+# Start the API server in foreground
+echo "Starting API server on port 8000..."
+exec uvicorn app.main:app --host 0.0.0.0 --port 8000