[Bug]: SegmentedGauge shows a spurious 1px coloured border with customColor

[soulcramer]

Outcome

When a customColor is passed to SegmentedGauge, no unintended coloured border appears on the indicator.

Problem

A thin (~1px) coloured border persists on the SegmentedGauge indicator when customColor is supplied. The border should not be rendered. The issue is cosmetic but visible at close inspection. Confirmed in #lbc-spark-android on 2026-07-30; a maintainer acknowledged it but no ticket was filed.

Context

The indicator drawing logic in SegmentedGauge likely applies a stroke or border derived from the custom colour that is not guarded or zeroed out when it should be absent.

• spark/src/main/kotlin/com/adevinta/spark/components/gauge/SegmentedGauge.kt — indicator rendering, look for stroke/border application when customColor is non-null.

Scope

• Remove or suppress the unintended border when customColor is set.

Acceptance criteria

• Passing any customColor to SegmentedGauge produces an indicator with no visible coloured border.
• A screenshot test (or an update to an existing one) covers the customColor variant and asserts no border is present.

Evidence

• Slack: https://adevinta.enterprise.slack.com/archives/C04QQEU3Y2H/p1785414293358709 — P.A.G., 2026-07-30
• spark/src/main/kotlin/com/adevinta/spark/components/gauge/SegmentedGauge.kt — indicator drawing code where the spurious border originates.