feat(editor): add Design-MD panel and complete i18n coverage
Design-MD panel — closes the last TS-vs-Rust parity gap:
- New floating op-editor-ui design_md_panel + design_md_markdown
renderer: collapsible theme/colour/typography/component/layout/
notes sections, colour swatches, inline markdown highlighting.
- op-editor-core: parse_design_md parser + panel UI state.
- Host: View-menu toggle, top-most paint + hit-test, drag,
.md import/export; bumps the vendor/jian DesignMdSpec pointer.
i18n coverage:
- Git panel, merge/conflict/error dialogs and GitError messages
routed through op-i18n; git locale tables split into
<base>_git.rs under the 800-line cap.
- Closed 10 app-wide hardcoded-string gaps (AI chat, Figma import,
file menu, layer context menu, property-panel fill, update /
file-picker / load-error dialogs, accesskit labels).
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