feat: functional gridfinity calculator app

memory-bank/systemPatterns.md

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+# System Patterns
+
+## Tech Stack
+- **Build Tool:** Vite
+- **Language:** TypeScript
+- **Styling:** Tailwind CSS
+- **Testing:** Vitest
+
+## Design Patterns
+- **Modular Logic:** Calculation logic is isolated in a pure TypeScript module (`src/calculator.ts`) for easy testing.
+- **Reactive UI (Vanilla):** Use DOM event listeners and a central `render()` or `update()` function to sync state to the UI.
+- **Unit Normalization:** All internal calculations should be performed in **millimeters**. Inputs in inches are converted immediately upon ingestion.
+
+## Directory Structure
+- `src/`: Source code.
+  - `calculator.ts`: Core business logic.
+  - `main.ts`: Entry point and DOM manipulation.
+  - `style.css`: Tailwind entry point.
+- `docs/`: Permanent documentation (PRD, Architecture).
+- `memory-bank/`: AI operational context.
+- `tests/`: Unit tests.
+
+## Calculation Constants (Defaults)
+- Grid Width/Depth: 42mm
+- Grid Height Unit: 7mm
+- Base Thickness: 4.8mm (typical baseplate height above surface)
+- Bin Lip/Bottom: 0.7mm (typical clearance/thickness to account for in vertical units)
+  - *Note: These defaults will be refined during implementation based on official specs.*