Markdown paste: replace heuristic-based detection with a single
deterministic check — only use HTML clipboard path when source is
another ProseMirror editor (identified by data-pm-slice attribute).
All other pastes (VS Code, text editors, terminals, .md files) parse
text/plain as Markdown via @tiptap/markdown.
Inline code: add box-decoration-break: clone and line-height: 2 so
multi-line inline code renders with proper spacing between lines.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>