Fix bad contrast for highlighted search results in tables

[gords2]

Fixes #9010

Problem

When a table row matches a search (e.g. searching in the CPU profiler), the whole row was highlighted with a fully opaque yellow/orange background while the row text kept its theme color (onSurface). In dark mode that's light text on solid yellow — unreadable.

Root cause

_table_row.dart blends searchMatchColorOpaque / activeSearchMatchColorOpaque over the row background. These were intended to be translucent (Colors.yellow.withOpacity(0.5)), but during the withOpacity → withValues migration in #8784 they became:

Colors.yellow.withValues(alpha: 255 / 2);

withValues takes alpha in the range 0.0–1.0, so 255 / 2 (= 127.5) clamps to 1.0 — fully opaque. The row tint stopped being translucent, so the underlying text was no longer legible. (This issue was filed 2025-03, ~2 months after #8784 landed the regression.)

Fix

Restore the intended translucency:

Colors.yellow.withValues(alpha: 0.5);
Colors.orangeAccent.withValues(alpha: 0.5);

The highlight is again a subtle 50% tint over the row background, so the theme-colored text stays readable in both light and dark themes. Added a regression test asserting these colors remain translucent.

Note

I couldn't run flutter test locally (no Dart/Flutter toolchain in my environment) — relying on CI to validate.

[gemini-code-assist]

Code Review

This pull request updates the alpha values for search match colors to 0.5 and adds corresponding regression tests to ensure they remain translucent. The reviewer notes that the variable names searchMatchColorOpaque and activeSearchMatchColorOpaque are misleading because they represent translucent colors, and suggests renaming them to better reflect their properties.

[gemini-code-assist]

[CONCERN] The variable names searchMatchColorOpaque and activeSearchMatchColorOpaque are misleading because they actually represent translucent colors (with an alpha of 0.5), whereas searchMatchColor and activeSearchMatchColor are the fully opaque versions. Consider renaming these variables to searchMatchColorTranslucent and activeSearchMatchColorTranslucent (or similar) to accurately reflect their properties and avoid confusion for future maintainers. Note that this would require updating their usages in _table_row.dart and other files.

References

1. The repository style guide emphasizes 'Meaningful Naming' under Code Quality constraints. ^(link)