fix: persist expanded text state of an item with query params

[Soxasora]

Description

Fixes #2818

After clicking show full text we now persist the expanded state of an item with full=true in the query params.
Coming back to an item with the full query param will present the item already expanded. Solves scroll restoration in long posts.

Screenshots

full-text.mp4

Additional Context

The nprogress loading bar appears when clicking show full text because we're doing a router action.

Checklist

Are your changes backward compatible? Please answer below:

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:

8

Did you use AI for this? If so, how much did it assist you?

No

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Note

Low Risk
Low-risk UI state change using shallow routing; may trigger the nprogress bar on expand as noted in the PR.

Overview
Expanded post text now survives navigation and reloads via a full=true query parameter instead of living only in component state.

useOverflow initializes show from router.query.full, and clicking show full text performs a shallow router.replace that merges full: true into the current query while still calling setShow(true). Hash-based expansion is unchanged in behavior but only forces show to true (it no longer collapses expanded text when the URL has no hash).

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[Soxasora]

The nprogress loading bar appears when clicking show full text because we're doing a router action.

This is an easy fix: shouldShowProgressBar in _app.js could check the new path against the current path, both void of their query params, instead of also comparing query params.