fix(logviewer): preserve URL lineNumber range across mount

[camd]

Summary

A shared logviewer URL like ?lineNumber=17657-19403 had its range stripped within milliseconds of page load, so the UI ended up selecting either the first error line (~17547) or just the range start (17657) — the range end was always lost.

Three interacting issues:

• ClassicLogViewer.jsx had a mount-time effect that fired onHighlightChange(highlight) while highlight was still its initial null from useLogViewer — so the parent's writeLineNumberParam(null) cleared the URL param before any of the URL-preservation logic could run.
• App.jsx only read urlLN[0] for initialLine and initialized highlight to null, dropping the range end on load.
• ClassicLogViewer.jsx's initialLine effect always called setHighlight([initialLine]) once the log finished fetching, which would clobber any restored range with a single line.

The fix snapshots the full URL range at mount, plumbs it through as initialHighlight (App → ClassicLogViewer → useLogViewer), and skips the mount run of the initialLine effect so it no longer overrides the range.

Test plan

• New regression test LogviewerUrlPreservation_test.jsx loads ?lineNumber=17657-19403, mocks the log + an error, and asserts window.location.search still contains the range after both fetches settle. A second test scans every history.pushState call and verifies none of them clobber the range.
• New unit test in useLogViewer_test.js covers the initialHighlight seed.
• All 1007 frontend tests still pass; biome lint clean on changed files.
• Manual: open /logviewer?...&lineNumber=A-B and confirm both the URL and the highlighted range survive the load.
• Manual: click and shift-click in the log, confirm the URL still updates with the single/range selection.
• Manual: open /logviewer?... (no lineNumber) and confirm the first error line is still auto-selected.

[codecov-commenter]

Codecov Report

❌ Patch coverage is 92.85714% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 82.83%. Comparing base (3519a51) to head (17e4cd8).

Files with missing lines	Patch %	Lines
ui/logviewer/ClassicLogViewer.jsx	75.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #9524      +/-   ##
==========================================
+ Coverage   82.75%   82.83%   +0.07%     
==========================================
  Files         604      604              
  Lines       34973    34977       +4     
  Branches     3261     3269       +8     
==========================================
+ Hits        28943    28972      +29     
- Misses       5661     5851     +190     
+ Partials      369      154     -215     

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