Feature/195 basic markdown support

[gramos-encora]

Description

This PR implements basic Markdown support in accordance with the requirements described in the related issue.

Summary of Implementation

• MVVM compliant: Parsing and preview rendering are handled in the ViewModel (NoteViewModel) and utility layer (MarkdownParser), keeping logic and UI strictly separated.

• No external libraries: Only native Android/Java classes used (e.g., SpannableString, Pattern, Matcher).

• Optional Preview Mode:

  • Activated via a toggle in the top menu (eye icon).
  • Inspired by SimpleMarkdown, but implemented from scratch.

• Supported Markdown Features (MVP):

  • #Heading 1 → Bold & larger font.
  • --underlined-- → Underlined text.
  • '*' Bullet points → Bullet-style prefix formatting.
  • Link Text → Clickable links with LinkMovementMethod.

• String resources: All user-facing strings (e.g., preview toggle) are localized through strings.xml.

• Legacy Compatibility: Notes use existing structures (IDs, timestamps) without modification.

• No SQLite / Fragments used.

Related Issue

Closes #195

[amarradi]

Hey @gramos-encora

after a long time, I finally got around to looking at your feature request. Unfortunately, I couldn't get it to work. I rebased it to the current state of development. Unfortunately, it doesn't work, but I also had to make a lot of changes and fix a lot of bugs in NoteEditActivity and NoteViewModel. Can you take a look at the branch called mdsupport? Maybe you can find what the bug is.