feat(engine): swap ACCENT_PRIMARY from cyan #6fc2ef to brick red #a54242

Project-wide palette shift at user request. Replaces the cyan
primary accent everywhere it surfaces — splash boot screen,
home menu glyphs, action chevrons, replay overlay banner +
scrub fill + chip border, achievement checkmarks, leaderboard
#1 indicator, radial menu fill, focus ring, card-back canonical
badge, etc. — with `#a54242` from the same base16-eighties
family as the existing pink suit colour.

Knock-on changes that all land in this commit per the
lockstep rule:

- ui_theme.rs: ACCENT_PRIMARY (#a54242), ACCENT_PRIMARY_HOVER
  (#c25e5e brightened companion), FOCUS_RING (same hue, 0.85
  alpha). Module-level palette comment + STOCK_BADGE_FG +
  CARD_SHADOW_ALPHA_DRAG doc strings updated to match.
- card_plugin.rs: card_back_colour(0) now returns the brick-red
  ACCENT_PRIMARY (was cyan). RED_SUIT_COLOUR_CBM swapped from
  cyan to lime #acc267 — the CBM alternative needs to stay
  hue-distinct from the new red-family primary, lime is the
  next-best non-red base16-eighties accent. text_colour doc
  + CBM tests renamed cyan→lime in lockstep
  (text_colour_color_blind_mode_swaps_red_suits_to_lime).
- card_face_svg.rs: BACK_ACCENTS[0] now "#a54242" (canonical
  Terminal back).
- splash_plugin.rs / ui_modal.rs / replay_overlay.rs /
  selection_plugin.rs: descriptive "cyan" comments swapped to
  "accent" / "primary-accent" wording so the doc strings stay
  decoupled from any specific hue. Future palette tweaks won't
  require comment churn.
- design-system.md: YAML token frontmatter updated (primary,
  surface-tint, suit-red-cb, primary-container,
  on-primary-container, inverse-primary). Palette table gains
  a project-specific `base08` slot for the new red. CTA /
  Selection / Card-back badge / Primary button / Bottom-bar
  active-icon / glow / CBM swap text all retuned. Historical
  references preserved (e.g. "Was cyan #6fc2ef before the
  2026-05-08 swap") so the audit trail stays in the spec.
- card_face_svg_pin.rs: rebaselined. Exactly one hash drift
  (back_0 — the canonical Terminal back's badge changed
  colour). Other 56 hashes identical (face SVGs don't
  reference the accent; back_1..4 use unchanged accents). The
  one-hash-drift signal confirms the change scope was
  surgical.

Workspace clippy + cargo test --workspace clean, 1184 passing.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

solitaire_engine/src/replay_overlay.rs

@@ -5,7 +5,7 @@
 //! - A "▌ replay" label on the left so the player knows the surface is
 //!   under playback control rather than live input.
 //! - A "MOVE N/M" progress chip in the centre, recomputed every frame
-//!   the cursor advances and bordered in cyan ACCENT_PRIMARY so it
+//!   the cursor advances and bordered in `ACCENT_PRIMARY` so it
 //!   reads as a discrete callout.
 //! - A "Stop" button on the right that aborts playback and returns
 //!   control to the player.
@@ -105,7 +105,7 @@ pub struct ReplayStopButton;
 #[derive(Component, Debug)]
 pub struct ReplayOverlayGameCaption;
 
-/// Marker on the cyan "fill" of the bottom-edge scrub bar. The
+/// Marker on the accent "fill" of the bottom-edge scrub bar. The
 /// `Node`'s `width` is rewritten every frame the cursor advances to
 /// `cursor / total` of the bar's full width, so the player has a
 /// continuous visual cue of how far through the replay they are.
@@ -250,7 +250,7 @@ fn spawn_overlay(
                     ..default()
                 })
                 .with_children(|row| {
-                    // Left: column with the cyan "▌ replay" headline
+                    // Left: column with the accent "▌ replay" headline
                     // above and a small `GAME #YYYY-DDD` caption below.
                     // The caption mirrors the mockup's right-anchored
                     // game identifier but stays visually grouped with
@@ -315,7 +315,7 @@ fn spawn_overlay(
 
                     // Right: Stop button. Tertiary variant — the
                     // action is available but not the loudest element
-                    // in the banner; the "Replay" cyan accent owns
+                    // in the banner; the "Replay" primary accent owns
                     // that slot. `spawn_modal_button` gives us hover /
                     // press paint and focus rings for free via the
                     // existing `UiModalPlugin` paint system.
@@ -425,7 +425,7 @@ fn update_progress_text(
     }
 }
 
-/// Repaints the bottom-edge cyan scrub fill to mirror cursor progress.
+/// Repaints the bottom-edge accent scrub fill to mirror cursor progress.
 /// Same change-detection guard as the text updaters — the overlay
 /// already early-exits when nothing moved, so an idle replay leaves the
 /// scrub bar's `Node` untouched.