[WC-3612]: Fix axis title config shape in charts

[r0b1n]

Pull request type

Bug fix (non-breaking change which fixes an issue)

Description

Fixes the axis title structure in the generated chart layout configuration, so axis titles are passed through as { text: "..." } instead of being wrapped an extra level.

Adds unit tests covering the shape of the generated layout, config and series options.

What should be covered while testing?

• Set X-axis and Y-axis labels on a chart widget and verify they render correctly.
• Verify charts without axis labels still render as before.

[github-actions]

AI Code Review

⚠️ Approved with suggestions — low-severity items only, safe to merge

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What was reviewed

File	Change
packages/shared/charts/src/utils/configs.ts	Removed double-wrapping of axis label: { text: xAxisLabel } → xAxisLabel directly
packages/shared/charts/src/utils/__tests__/configs.spec.ts	New unit test file covering layout, config, and series option merging
packages/pluggableWidgets/bubble-chart-web/e2e/…-snapshots/*.png	Updated visual baselines (2 files)
packages/pluggableWidgets/line-chart-web/e2e/…-snapshots/*.png	Updated visual baselines (3 files)

Skipped (out of scope): dist/, pnpm-lock.yaml

CI checks: could not fetch automatically — please confirm all checks pass before merging.

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Findings

⚠️ Low — Missing CHANGELOG entries for bubble-chart-web and line-chart-web

Files: packages/pluggableWidgets/bubble-chart-web/CHANGELOG.md, packages/pluggableWidgets/line-chart-web/CHANGELOG.md
Note: Both widget packages had their E2E visual baselines updated because the axis label rendering changed (the core fix lives in shared/charts, but it is observable behaviour in these widgets). The [Unreleased] sections in both CHANGELOGs are empty. A user-facing bug fix entry belongs there. The shared/charts package is private and has no CHANGELOG, so no entry is needed there.
Fix: Add a ### Fixed entry under [Unreleased] in each widget's CHANGELOG.md, e.g.:

### Fixed

- We fixed an issue where X-axis and Y-axis labels were not rendered correctly on charts.

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Positives

• The root cause is cleanly identified: callers already pass { text: "…" } objects (confirmed across all seven widget consumers), so the extra wrapping in getCustomLayoutOptions was creating { text: { text: "…" } } — the two-line fix is exactly the right scope.
• The new unit tests directly assert the shape of the generated Plotly Layout object at each level of merging (getCustomLayoutOptions, getModelerLayoutOptions, getModelerConfigOptions, getModelerSeriesOptions), closing the gap that allowed this bug to go undetected.
• Parametrised it.each for the four gridLinesMode values is a clean and exhaustive approach.
• Updated visual baselines are committed alongside the fix — reviewer can visually verify the label rendering is now correct.