feat: redesign LineSegmentFlow + dev improvements

- LineSegmentFlow: LobeHub brand icons, concave left curves, glow effects
- Dark mode: line colors adapt, animated lines glow in dark theme
- Vite: enable LAN access (host: 0.0.0.0)
- VSCode: workspace settings for performance optimization
- Toast: redesign with icons, progress bar, better animations

Makefile

@@ -19,7 +19,7 @@ run: build
 	./$(BUILD_DIR)/$(BINARY_NAME)
 
 # Development: backend + frontend (requires air + pnpm)
-dev: dev-backend dev-frontend
+dev: dev-frontend dev-backend
 
 # Go backend with hot reload (requires: go install github.com/air-verse/air@latest)
 dev-backend: