[gcko]

PR checklist

• Ensure you have added or ran the appropriate tests for your PR.
• DCO signed

What type of PR is this?

refactor

What this PR does / why we need it:

useThemeColors() rebuilt its return object and all five nested sections (background, text, border, status, interactive) on every call. Any consumer that placed a section in a useMemo / useCallback dependency array would have been invalidated on every render.

This hoists the light and dark values into two module-level tables and returns a single useMemo keyed on the resolved mode and the MUI theme. Section references are now stable for as long as the mode is unchanged, and flipping light → dark → light returns the original references.

Color values are unchanged. All 20 leaves in each mode were mechanically compared against the previous ternaries.

Which issue(s) this PR fixes:

Closes DRC-3328

Special notes for your reviewer:

• This is hygiene, not a measured perf win. No in-repo consumer currently threads a section into a dependency array, so no metric moves today. The ticket's April 28 comment recommended deferring until RUM telemetry landed; this ships it anyway as a cheap, behaviour-preserving fix to a public hook.
• Public type change: ThemeColors leaves were previously literal unions inferred from the as const palette (for example "#171717" | "#FFFFFF"). They are now string. This is a widening, so assignments into sx, color, or any string slot are unaffected. Workspace type-check (root, ui, storybook) passes.
• isDark is always false on first render (the mounted guard), so the memo keys on the resolved mode rather than the raw inputs. The tests assert identity only within a mode.
• The test file's mocked MUI theme is hoisted to a single constant via vi.hoisted so the top-level memo is observable. Production MUI already memoizes the theme object.

Verification:

pnpm vitest run packages/ui/src/hooks packages/ui/src/components/lineage/__tests__/LineageView.test.tsx packages/ui/src/components/errorboundary
  Test Files  11 passed (11)
       Tests  127 passed (127)
pnpm type:check   # root + @datarecce/ui + @datarecce/storybook: clean
pnpm biome check  # both files: clean

Does this PR introduce a user-facing change?:

NONE

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