Structured Doc Editor v0.13.0

What's Changed

• perf: optimize large single-document editing by @SWBaek in #217
• perf(vscode): minimize persistence text edits by @SWBaek in #218
• perf(vscode): cache modified token offsets by @SWBaek in #219
• perf: bound large-document persistence and editor work by @SWBaek in #220
• perf(editor): share the code-block language listbox by @SWBaek in #221
• test(ui): stabilize code language contract by @SWBaek in #223
• fix(release): prepare v0.13.0 package verification by @SWBaek in #225

Full Changelog: v0.12.2...v0.13.0