Fix new comments navigator duplicate counts

[Soxasora]

Description

Fixes #2606
When navigator receives a new comment ref, the deduplication process only checks if the exact ref received is already present in the commentRefs array. When a comment gets collapsed and uncollapsed, its ref dies and the comparison would just fail.

The fix involves making the comment counter aware of stale (disconnected) refs and refreshing it on every action.
This way, the navigator gets rid of stale refs and the counter will always be truthful to what is shown to the user; fixing duplicate counts (collapsing and uncollapsing), and stale counts (collapsing).

Screenshots

tbd

Additional Context

This is another reminder for me to refactor the outlining system, since the outlining effect shouldn't run on every collapse/uncollapse.

Checklist

Are your changes backward compatible? Please answer below:

For example, a change is not backward compatible if you removed a GraphQL field or dropped a database column.
Yes

On a scale of 1-10 how well and how have you QA'd this change and any features it might affect? Please answer below:
7, scrolling to a comment, collapsing and uncollapsing works correctly.

For frontend changes: Tested on mobile, light and dark mode? Please answer below:
n/a

Did you introduce any new environment variables? If so, call them out explicitly here:
n/a

Did you use AI for this? If so, how much did it assist you?
no

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Note

Make the comments navigator robust to disconnected refs and add cleanup to untrack comments, ensuring accurate new-comment counts.

• Comments Navigator (components/use-comments-navigator.js):
  • Filter out disconnected refs before counting in throttleCountUpdate.
  • In untrackNewComment, update count even if the ref is missing; always call throttleCountUpdate after processing.
  • In scrollToComment, handle missing nodes by triggering a count refresh; update dependencies.
• Comment component (components/comment.js):
  • Add cleanup to useEffect to call navigator.untrackNewComment(ref, { includeDescendants: true }) when effect cleans up, preventing stale tracking.

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[Soxasora]

I thought of a simpler way to fix this: we can untrack the comment on unmount (which collapsing does) and add a check for disconnected refs in the comment counter.

This way, every time there's an invalid ref being passed, or an action, the navigator cleans itself from stale refs.