bug: Nile --text-muted fails 4.5:1 text contrast on raised surfaces #285

Affected file: frontend/src/styles/tokens.css (Nile/dark theme block, --text-muted: #948970)

Description: --text-muted (#948970) was contrast-checked against the base --surface (#0d2422) at 4.70:1, passing the 4.5:1 WCAG 2.2 text floor. It was not checked against --surface-container-high (--bg-raised, #16403c), the elevated/raised surface token also introduced by this design system for cards, modals, and drawers, where it drops to 3.31:1, failing the floor.

Failure scenario: Once a later Material Design stage renders muted/secondary text (timestamps, byline text, helper copy) inside a card, modal, or other raised container in the Nile (dark) theme, that text falls below the accessibility floor for the project's stated hard-floor requirement (WCAG 2.2 AA).

Recommended fix: Lighten Nile's --text-muted to at least #afa58b, which restores a compliant 4.68:1 against --surface-container-high (independently recomputed and confirmed) while remaining well above 4.5:1 against the base --surface too.

Found via an adversarial code review (Gemini 3.1 Pro) of PR #281, independently verified via the WCAG 2.2 relative luminance formula. Not fixed in PR #281 since Stage 1 ships no component that renders --text-muted on a raised surface yet; worth resolving before that combination appears in a later stage.