Add Markdown rendering for imported .txt files and vocabulary notes to improve readability and study organization

Why it is useful & Who would benefit: When importing custom articles, web novels, or books as raw .txt files, the text can often look monotonous and dense. Markdown support would allow language learners to see clear chapter headers (#), italicized contexts (*text*), and bolded idioms (**text**). Furthermore, allowing Markdown in custom vocabulary notes means learners can neatly organize multiple definitions and bulleted example sentences. This greatly benefits active language learners who rely on structured, easy-to-read materials and custom notes for effective daily practice. How it should work: Reader Rendering: When a user opens a .txt file containing basic Markdown tags, the app's reader engine should automatically parse and render them with the correct visual formatting (headers, bold, italics) alongside the parallel translation. Formatted Notes: The section where users save words and add custom translations or notes should support basic Markdown syntax. This would allow users to use bullet points for example sentences and bold text for grammar roots, making their vocabulary reviews much more efficient.