feat(core): line number gutter with current line highlight
- .me-gutter rendered alongside textarea, sync-scrolls with content
- .me-gutter-active highlights the line containing the cursor
- config.lineNumbers (default true) to toggle
feat(core): smart Enter auto-formatting
- List continuation: '- ' / '1. ' auto-insert on Enter at end of list item
- Ordered list auto-increment: '1.' → '2.'
- Quote continuation: '> ' auto-insert on Enter at end of quote line
- Empty list/quote item: Enter removes the marker (end list)
feat(core): bracket/quote auto-close
- (), [], {}, <>, "", '', ``, **, __ auto-close pairs
- Selection wrapping: select text then press ( → wraps as (text)
- config.autoBrackets (default true) to toggle
feat(core): drag & drop file support
- Drop image files → auto base64 inline insert 
- Drop text/code files → insert file contents
- Drop external text from browser → insert at cursor
feat(core): outline/TOC panel
- Extracts headings from rendered HTML preview
- Nested tree with indentation by heading level
- Click to scroll-jump in both preview and textarea
- config.outline (default false) to toggle
style: gutter, outline panel, current line highlight CSS
test: 11 new tests for gutter, auto-format, bracket close, outline (532 total)
chore: bump version 0.1.6 → 0.1.7 across all files, site, types
thzxx