docs: add README and MIT license

- add comprehensive README with installation instructions
- include development setup and mise task documentation
- specify system requirements and permission needs
- add MIT license for open source distribution

Author: mfyuu

LICENSE

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+MIT License
+
+Copyright (c) 2026 mfyuu
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+SOFTWARE.

README.md

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+# PressViz
+
+A native macOS app for visualizing keyboard presses.
+
+## Installation
+
+1. Download the latest DMG from [Releases](https://github.com/mfyuu/press-viz/releases)
+2. Open the DMG file
+3. Drag PressViz to your Applications folder
+4. Launch PressViz from Applications
+
+### Requirements
+
+- macOS 26.2+
+
+### Permissions
+
+PressViz requires **Accessibility** permission to monitor keyboard input.
+
+1. Open System Settings > Privacy & Security > Accessibility
+2. Enable PressViz
+
+## Development
+
+### Prerequisites
+
+- Xcode
+- [mise](https://mise.jdx.dev/) (optional, for task runner)
+- [create-dmg](https://github.com/create-dmg/create-dmg) (for DMG creation)
+
+### Build
+
+```bash
+# Debug build
+mise run build
+
+# Release build
+mise run release
+
+# Clean
+mise run clean
+```
+
+### Version Management
+
+```bash
+# Show current version
+mise run version
+
+# Set version
+mise run version:set 0.2.0
+```
+
+### Create DMG
+
+```bash
+mise run dmg
+```
+
+## License
+
+MIT