feat: functional gridfinity calculator app

memory-bank/activeContext.md

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+# Active Context
+
+## Current Status
+- Initializing the project environment.
+- Documentation phase (Memory Bank & Blueprint).
+
+## Recent Changes
+- Created `memory-bank/projectBrief.md`.
+- Created `memory-bank/productContext.md`.
+
+## Current Focus
+- Completing Memory Bank initialization.
+- Drafting PRD and Architecture.
+- Setting up the Vite/TypeScript/Tailwind environment.
+
+## Active Decisions
+- Using **Vite** for the build tool.
+- Using **Vanilla TypeScript** to avoid framework overhead.
+- Using **Vitest** for unit testing calculation logic.
+- Target: A single-page application that can be built into a self-contained output.

memory-bank/productContext.md

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+# Product Context
+
+## Why this project exists?
+Gridfinity is a popular modular storage system. While the standard is well-defined (42x42x7mm), users often need to:
+1. Figure out how many baseplates fit in a drawer.
+2. Determine the maximum height of bins for a specific drawer depth.
+3. Scale the system slightly to perfectly fill a drawer that doesn't fit a whole number of 42mm grids.
+
+## User Experience
+- **Input-First:** Users should immediately see where to enter their dimensions.
+- **Instant Feedback:** Results should update as they type.
+- **Flexibility:** Toggle between mm and inches easily.
+- **Precision:** Clear output showing "Full Grids" and "Vertical Units".
+
+## Success Criteria
+- Accurately converts between units.
+- Correctly calculates bin height while accounting for baseplate/bin-bottom thickness.
+- Provides clear instructions for "fractional" fits (e.g., if a drawer is 100mm, it fits 2.38 grids).

memory-bank/progress.md

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+# Progress Tracking
+
+## Milestones
+- [ ] Initial Environment & Docs Setup
+- [ ] Core Calculation Engine
+- [ ] Web UI & Integration
+- [ ] Final Build & Polish
+
+## Todo List
+- [x] Create project structure
+- [x] Initialize Memory Bank documents
+- [ ] Create Blueprint documents (PRD, Architecture)
+- [ ] Project setup (Vite, TS, Tailwind, Vitest)
+- [ ] Implement `src/calculator.ts`
+- [ ] Write tests in `src/calculator.test.ts`
+- [ ] Implement `index.html` UI
+- [ ] Implement `src/main.ts` glue code
+- [ ] Verify build output

memory-bank/projectBrief.md

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+# Project Brief: Gridfinity Calculator
+
+A simple, lightweight web-based calculator for Gridfinity baseplates and bins.
+
+## Core Requirements
+- Enter drawer/container dimensions (width, height, depth).
+- Support for both inches and millimeters.
+- Custom overrides for Gridfinity specifications (default 42x42x7mm).
+- Calculate required baseplates (full grids).
+- Calculate bin vertical unit height (7mm increments), accounting for base thickness.
+- No heavy frameworks (Vanilla TS/Vite).
+- Single-page optimized build.
+
+## Goals
+- Provide an accurate and easy-to-use tool for Gridfinity makers.
+- Allow for non-standard scaling to fit specific drawer sizes perfectly.
+- Clean, responsive UI with Tailwind CSS.

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.*