Add simple browser-based todo list

[one3883]

Motivation

• Provide a minimal, single-file todo list UI that satisfies a quick "rough todo" request with no build steps or external dependencies.
• Keep data client-side so the app is immediately usable in the browser and persists across reloads using browser storage.

Description

• Added index.html implementing a lightweight single-page todo app with an input, add button, and a todo list container.
• Implemented add, complete (checkbox), and delete (❌) interactions in vanilla JavaScript, including Enter-key support via input keydown handling.
• Persisted todos to localStorage under the key rough-todos and implemented render()/save() helpers to keep UI and storage in sync.
• Included basic responsive styling and a clean card-based layout using in-file CSS for immediate use without additional assets.

Testing

• Served the page locally with python3 -m http.server 4173 and confirmed the server responded successfully.
• Ran a Playwright automation script that opened the page, added sample todos, toggled a completion checkbox, and captured a screenshot, which completed successfully.
• All automated checks (server start and browser automation) passed and produced the expected UI behavior and artifact.

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Codex Task