[jonaraphael]

Dark High Contrast was classified as a light theme, so CSV used its light datatype palette on a dark background. This change classifies it correctly while preserving the user's selected default, cool, or warm datatype palette. Both high-contrast variants continue to honor csv.columnColorMode: datatype colors remain the default, and theme foreground remains an explicit local choice. No settings or commands are added.

The accessibility stylesheet applies only to high-contrast body classes. It adds theme-aware borders, menus, Find/Replace controls and selection/find outlines without forcing cell foregrounds or covering datatype colors with selection fills. Ordinary light/dark colors retain their previous values. Inherited color variables allow theme transitions without replacing the webview, cell DOM, draft, focus or caret. The palette calculation itself is unchanged.

Addresses #92.

Validation:

• Node 20.20.0: npm run compile, npm test — all 173 tests pass; npm run lint — 0 errors, 87 existing warnings; git diff --check passes.
• Actual provider regressions cover CSV/TSV, all three palettes and both modes, all four theme kinds, headers, body/append cells, serialized/on-demand chunks and metadata/header-off rendering. Scope tests enforce HC-only accessibility rules and unchanged ordinary chrome values.
• The shipped webview script is exercised with a live multiline draft: theme classes change while DOM identity, focus, caret, source text and version remain unchanged.
• Chromium fixture QA compares actual generated provider HTML and shipped assets with immutable parent Make multiline and manual column sizing predictable #112. Ordinary text/background/border/menu/Find colors match the previous implementation across all palettes and both modes. The two-pane fixture's native focus-ring differences are separate from authored colors.
• With the packaged stylesheet confirmed loaded, Chromium checks preserve every data-cell foreground across all three palettes in both HC variants; explicit theme mode uses the supplied foreground. HC selection/find states retain those colors and use editor-background fills with visible outlines.
• In-editor theme transitions preserve a live multiline draft, DOM/widget identity, caret position 5 and source/version 1 across all four classes. A deferred edit remains pending across transitions, then applies exactly once when released; disk text remains unchanged.
• Browser QA uses simulated VS Code theme variables and host callbacks; it does not claim native VS Code high-contrast paint or a contrast guarantee for every customized theme.

Independent orchestrator review and integration: inspected the final delta and both renderer conflict resolutions. The combined candidate 8b2860e passes compile, all 529 tests, lint (0 errors; 86 existing warnings) and diff checks. Chromium checks cover frozen selection and actual Find matches, all four theme transitions, numeric/date/boolean filtered source identities, and live/deferred multiline edits. Frozen offsets, filter-bar inset, serial/header actions, popup geometry, arrow scrolling and existing draft guards remain intact.

Exact-head GitHub CI succeeds and this PR is mergeable against its current stacked base. The narrowed palette policy is cleared for human review; no merge or release has been performed.