fix: vertically center chart tooltip and legend markers

[ClaudioGSDB]

Description

Chart series markers weren't vertically centered against their label in tooltips (and legends) - the marker sat low/high depending on type, because each marker carried a hardcoded margin-block-start to fake alignment under a top-aligned (flex-start) row.

Fix - center the row and drop the magic margins so alignment is geometric:

• chart-series-details: the key row uses align-items: center instead of flex-start.
• chart-legend: legend item row align-items: center.
• chart-series-marker: removed margin-block-start from .marker, .marker--line, and .marker--dashed.

Affects chart tooltips and legends (shared marker), so expect visual-snapshot diffs across those. Note: multi-line tooltip keys now center the marker against the whole block rather than the first line.

Related links, issue #, if available: n/a

How has this been tested?

Review checklist

The following items are to be evaluated by the author(s) and the reviewer(s).

Correctness

• Changes include appropriate documentation updates.
• Changes are backward-compatible if not indicated, see CONTRIBUTING.md.
• Changes do not include unsupported browser features, see CONTRIBUTING.md.
• Changes were manually tested for accessibility, see accessibility guidelines.

Security

• If the code handles URLs: all URLs are validated through the checkSafeUrl function.

Testing

• Changes are covered with new/existing unit tests?
• Changes are covered with new/existing integration tests?

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 97.59%. Comparing base (cfd3761) to head (21d1e3c).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #4723   +/-   ##
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  Coverage   97.59%   97.59%           
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  Files         950      950           
  Lines       30690    30690           
  Branches    11254    11254           
=======================================
  Hits        29953    29953           
  Misses        730      730           
  Partials        7        7           

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[pan-kot]

This change breaks alignment when drill-down feature is used.