refactor(pages): replace hardcoded colors with theme tokens

[volcano303]

Summary

• replace hardcoded page-level colors with existing theme tokens across Home, Dashboard, Issues, PR, Repository, Onboard, and Discoveries pages
• add palette.alert.warningBg, palette.alert.warningBorder, and palette.alert.warningText for warning alert styling
• update page tabs, borders, surfaces, scrollbar thumbs, and status chips to use semantic theme values instead of inline color literals

Type of Change

• Refactor
• Bug fix
• New feature
• Documentation
• Other (describe below)

[anderdc]

The page-level token swaps are good — those files should be using the theme tokens we already have. Two things to fix:

• Drop the palette.alert addition from theme.ts. Three tokens for one component isn't worth a new palette section. Use alpha(STATUS_COLORS.warningOrange, 0.08) and friends inline, or use the existing status.warning / status.warningOrange tokens directly.
• text.disabled doesn't exist in the theme. Used in 4 places in RepositoriesPage.tsx. The palette has text.primary, text.secondary, text.tertiary — pick the closest match or use alpha(theme.palette.text.primary, 0.3) to preserve the original appearance.

Also no CI checks ran on this branch — push or retrigger so build/format pass before re-review.

[anderdc]

Previous feedback on palette.alert and text.disabled is addressed — those are gone.

New issue: this PR bundles two unrelated changes. The title says "replace hardcoded page colors with theme tokens" but half the diff is a new ensureArray / useArrayApiQuery API safety layer across 7 API files. These should be separate PRs — the API changes touch shared data-fetching hooks and need their own review and testing.

Split this into:

1. Theme token swaps (pages only)
2. ensureArray / useArrayApiQuery API hardening (separate PR)

[anderdc]

API changes split out, pages-only now. CI passes. Looks good.