Act as a senior frontend engineer. Create a complete, single-page React application called "Twinventory" - a digital twin inventory platform for small businesses.

Tech Stack & Environment:

• React 19: Use Functional Components and Hooks.
• Tailwind CSS: Use via CDN in index.html.
• Icons: lucide-react.
• Charts: recharts.
• AI SDK: @google/genai (for Gemini 3 integration).
• Structure: Flat structure (no src folder), use index.html, index.tsx, App.tsx.

Visual Identity:

• Theme: Clean, professional SaaS look.
• Colors: Background slate-50, Primary indigo-600, Success emerald-500, Warning amber-400, Danger red-500.
• Typography: Inter font family.
• Components: Rounded corners (rounded-xl for cards), subtle borders (border-slate-200), soft shadows.

Core Data Types (types.ts):

• InventoryItem: id, sku, name, category, stockLevel, reorderPoint, price, location, lastRestock, salesVelocity, trend (up/down/stable), history (number array).
• SimulationResult: scenario, prediction, impactScore (0-100), riskLevel (Low/Med/High), suggestedAction.
• ViewState: 'landing' | 'dashboard'.

Data (constants.ts):

• Create MOCK_INVENTORY with at least 10 items across categories like Apparel, Electronics, Home Goods. Ensure a mix of stock levels (Critical, Low, Healthy).

Services (services/geminiService.ts):