Update README with Docker deployment instructions and auth features

- Added comprehensive Docker Compose deployment section as recommended method
- Documented automatic database migrations and persistent storage
- Updated architecture section to mention SQLite auth system
- Added new User Experience section highlighting session management
- Reorganized development setup with local database migration instructions

🤖 Generated with [Claude Code](https://claude.ai/code)

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

Dockerfile

@@ -79,7 +79,7 @@ RUN cargo build --release --bin backend
 FROM alpine:latest
 
 # Install runtime dependencies
-RUN apk add --no-cache ca-certificates tzdata
+RUN apk add --no-cache ca-certificates tzdata sqlite
 
 # Copy frontend files to temporary location
 COPY --from=builder /app/frontend/dist /app/frontend-dist
@@ -99,9 +99,9 @@ RUN echo '#!/bin/sh' > /usr/local/bin/start.sh && \
     echo 'echo "Ensuring database directory exists..."' >> /usr/local/bin/start.sh && \
     echo 'mkdir -p /db && chmod 755 /db' >> /usr/local/bin/start.sh && \
     echo 'echo "Running database migrations..."' >> /usr/local/bin/start.sh && \
-    echo 'sqlx migrate run --database-url "sqlite:/db/calendar.db" --source /migrations || echo "Migration failed but continuing..."' >> /usr/local/bin/start.sh && \
+    echo 'sqlx migrate run --database-url "sqlite:///db/calendar.db" --source /migrations || echo "Migration failed but continuing..."' >> /usr/local/bin/start.sh && \
     echo 'echo "Starting backend server..."' >> /usr/local/bin/start.sh && \
-    echo 'export DATABASE_URL="sqlite:/db/calendar.db"' >> /usr/local/bin/start.sh && \
+    echo 'export DATABASE_URL="sqlite:///db/calendar.db"' >> /usr/local/bin/start.sh && \
     echo '/usr/local/bin/backend' >> /usr/local/bin/start.sh && \
     chmod +x /usr/local/bin/start.sh