gram: docs

> ./openspec/changes/paragraph-border-rendering/design.md

# Design: Paragraph Border Rendering

## Architecture

Both border types flow through the same pipeline:

1. **Parser** (`docx/paragraphParser.ts`) — already parses `between` and `bar` from `w:pBdr`
2. **ProseMirror schema** (`ParagraphExtension`) — already stores borders in paragraph attrs
3. **Layout-painter** (`renderParagraph.ts`) — currently only renders `top/right/bottom/left` borders

### `w:bar` implementation

Simple: render a vertical CSS border on the left edge of the paragraph div.

border-left: