Auto-Save Markdown to LocalStorage

**Description:**
Add an auto-save feature that stores the user’s Markdown text in the browser’s localStorage every few seconds (or on input).

When the user returns to the page, the last text should automatically load.

Add a small toast message: “Draft auto-saved!”

**Expected result:**
The user never loses unsaved markdown text after reloading the page.

Start at the page containing the Markdown text input and identify where its value is read on input and initialized when the page loads. Done means the text is saved to browser localStorage, restored after reload, and the “Draft auto-saved!” toast appears.

Written by the indexing model from the issue text.