v1.13.0: minimal top bar, spec navigation, changed-only

Signed by Mozilla for Firefox 140 or later, plus an unpacked build for Chrome, Edge and Brave.

Firefox: click markdown-pr-sentence-comments-1.13.0.xpi below and allow github.com to install the add-on.

Chrome, Edge, Brave: download markdown-pr-sentence-comments-chrome-1.13.0.zip, unzip it to a folder you keep, open chrome://extensions, switch on Developer mode, and click Load unpacked. For an update, replace the folder contents and click the reload icon.

New in this version:

• Quieter top bar: only the tabs and one pair of arrows that walk the spec outline, requirement by requirement. The auto-render switch moved into the panel header.
• Spec first, and the panel opens on the Outline by itself.
• Jump to the proposal once the Markdown files have rendered.
• Changed rows are marked: every proposal section, requirement, scenario and task this PR touched carries a dot, and Changed only hides the rest. A follow-up PR that edits a merged spec and ticks off a task shows exactly those.

Based on chienyuanchang/rich-diff-comments (MIT).