feat(engine): revert to traditional 2-colour deck with saturated red + near-white

Per player feedback after the brief 4-colour-deck experiment:
"can we make the card suit colors the same as a regular
solitaire game would." Reverts the 4-colour split (`62b61cc`)
and bumps both 2-colour hues to read more like a real
Microsoft-Solitaire-on-dark-mode deck.

### Constants

- `RED_SUIT_COLOUR`: `#fb9fb1` (Terminal pink, then briefly
  hearts-only) → `#e35353` (saturated red). More chromatic, less
  pastel; reads as "the red suit" rather than "a Terminal-
  themed pink." Visually distinct from `ACCENT_PRIMARY`
  `#a54242` (the brick-red CTA accent) so chrome and suit don't
  collapse to the same hue.
- `BLACK_SUIT_COLOUR`: `#d0d0d0` (matched `TEXT_PRIMARY`) →
  `#e8e8e8` (near-white). Bumped slightly brighter so it reads
  as a chromatic-neutral counterpart to the new saturated red,
  not as "the same gray as body text." `TEXT_PRIMARY_HC`
  (`#f5f5f5`) is still brighter for the high-contrast boost
  path.
- `RED_SUIT_COLOUR_HC`: `#ff8aa0` (pinkish boost matching the
  v0.21.0 pink default) → `#ff6868` (brighter saturated red).
  Now reads as "more chromatic" than the new default red, not
  "less saturated."
- `DIAMOND_SUIT_COLOUR` and `CLUB_SUIT_COLOUR` deleted — the
  4-colour split is gone, hearts/diamonds re-pair under
  `RED_SUIT_COLOUR` and clubs/spades under
  `BLACK_SUIT_COLOUR`.

### `card_face_svg.rs`

- Module-level constants collapse from four (`SUIT_HEART` /
  `SUIT_DIAMOND` / `SUIT_CLUB` / `SUIT_SPADE`) back to two
  (`SUIT_RED` / `SUIT_DARK`) at the new saturated-red /
  near-white values.
- `suit_paint()` reverts to the 2-colour pairing: hearts
  filled-red, diamonds outlined-red, spades filled-near-white,
  clubs outlined-near-white. Filled-vs-outlined glyph
  differentiation stays the always-on CBM fallback.

### `card_plugin.rs`

- `text_colour()` reverts to a `card.suit.is_red()`
  bifurcation. Comment block updated to reflect the new
  truth table: red suits → saturated red (or CBM lime / HC
  brighter red); dark suits → near-white (or HC brighter
  near-white).

### Tests

Test block restructured back to the pre-4-colour shape: two
red/black pairing tests instead of one 4-colour distinctness
test. CBM/HC compose tests retuned to the 2-colour world (red
suits compose, dark suits compose; no separate diamonds-immune
or clubs-immune cases). 1191 passing / 0 failing — net 0 from
the prior commit (3 tests removed: the 4-colour distinctness
test + the diamonds/clubs-immune test; 2 tests added back: the
red-pairing + dark-pairing tests; existing tests amended to
new colour assumptions).

### `card_face_svg_pin`

All 52 face hashes drift (every suit's colour shifted); 5 back
hashes unchanged. Surgical rebaseline.

### `design-system.md`

§Suit Colors retitled "Two-color traditional pairing", table
updated with the new hex values, CBM section text simplified
back to red→lime swap on both red suits.

Workspace clippy clean.

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

solitaire_engine/src/assets/card_face_svg.rs

@@ -30,18 +30,14 @@ pub const TARGET: UVec2 = UVec2::new(256, 384);
 
 const BG_FACE: &str = "#1a1a1a"; // BG_ELEVATED — face background
 
-// Four-colour deck: each suit picks up its own base16-eighties
-// accent so a player scanning the table can distinguish the suit
-// by hue alone. Faster recognition than the 2-colour traditional
-// red/black scheme; common in poker-room decks and online card
-// games. The outlined-glyph differentiation (♦ ♣ outlined, ♥ ♠
-// filled) is preserved on top of the colour split as the
-// always-on colour-blind fallback per `design-system.md`
-// §Accessibility.
-const SUIT_HEART: &str = "#fb9fb1"; // pink (base08 / RED_SUIT_COLOUR)
-const SUIT_DIAMOND: &str = "#ddb26f"; // gold (base09 / STATE_WARNING)
-const SUIT_CLUB: &str = "#acc267"; // lime (base0A / STATE_SUCCESS)
-const SUIT_SPADE: &str = "#d0d0d0"; // foreground gray (base05 / TEXT_PRIMARY)
+// 2-colour traditional pairing — hearts + diamonds share a
+// saturated red, clubs + spades share a near-white. Mirrors the
+// "Microsoft Solitaire on dark mode" feel of a real card deck.
+// Brief 4-colour-deck experiment between v0.21.0 and this commit
+// reverted; the always-on filled-vs-outlined glyph differentiation
+// (♦ ♣ outlined, ♥ ♠ filled) carries the always-on CBM fallback.
+const SUIT_RED: &str = "#e35353"; // matches `RED_SUIT_COLOUR`
+const SUIT_DARK: &str = "#e8e8e8"; // matches `BLACK_SUIT_COLOUR`
 
 const BACK_BG: &str = "#151515";
 const BACK_SCANLINE: &str = "#1a1a1a";
@@ -156,10 +152,10 @@ enum GlyphPaint {
 
 fn suit_paint(suit: Suit) -> (&'static str, GlyphPaint) {
     match suit {
-        Suit::Hearts => (SUIT_HEART, GlyphPaint::Filled),
-        Suit::Diamonds => (SUIT_DIAMOND, GlyphPaint::Outlined),
-        Suit::Spades => (SUIT_SPADE, GlyphPaint::Filled),
-        Suit::Clubs => (SUIT_CLUB, GlyphPaint::Outlined),
+        Suit::Hearts => (SUIT_RED, GlyphPaint::Filled),
+        Suit::Diamonds => (SUIT_RED, GlyphPaint::Outlined),
+        Suit::Spades => (SUIT_DARK, GlyphPaint::Filled),
+        Suit::Clubs => (SUIT_DARK, GlyphPaint::Outlined),
     }
 }