feat(new tool): Markdown Format Converter

[erichschroeter]

Implements #485

This PR adds the Markdown Format Converter tool. It decouples format parsing from rendering by introducing custom Abstract Syntax Tree (AST) tokenizers for each supported format.

Key Features

• Strategy Pattern Enhancements: Added lex(input: string): Token[] to the ConverterStrategy interface.
• Custom Format Parsers (AST-based):
  • Slack Strategy: Normalizes Slack-specific markers (*bold*, _italic_, ~strike~, <url|text>) and converts single-line bold texts into headings before parsing.
  • Jira Strategy: Processes ordered/unordered lists, {code}, {quote}, headings, !image!, and bracket links into GFM before lexing.
  • Logseq Strategy: Normalizes Logseq outline bullets, strips internal metadata, and handles the logseq.order-list-type:: number block property to correctly build GFM ordered lists.
• UI & Locales:
  • Added a Source Format dropdown next to the Target Format dropdown.

Validation & Testing

• Added cross-format test suites verifying Slack-to-Jira, Jira-to-Slack, and Logseq-to-GitHub conversions.

Warning

I have not tested Jira.