fix(themes): P2 contrast floors retuned + gated across 9 themes (item 28b done)

18 hex retunes, hue-preserving OKLCH minimal raises except where the
upstream palette defines a canonical value: muted lifted to >= 2.0 on
lumon/white/retro-82/everforest (solved), gruvbox (bg4 #7c6f64), nord
(#616e88, the community comment-brightening), catppuccin-latte
(overlay1 #8c8fa1); text-on-surface >= 4.5 via surface nudges
(ristretto darker, latte lighter); accentAlt >= 3.0 (latte, summer-day
darkened); warn >= 2.5 — the bar's battery tint — darkened on the
light bases (latte, rose-pine dawn, summer-day) and flexoki-light's
four status colors moved to their canonical light-mode 600 series.

check-theme-contrast.py now gates all four adopted floors (7 pairings
x 21 themes, green). good/bad stay audit-only — identity themes sit at
2.0-2.3 there by design, so no exemption mechanism was needed. The
design audit's contrast findings drop 20 -> 1 (miasma's earthy `bad`,
kept as identity). Item 28 slice (b) complete.

Verified: V0, checks.theme-contrast green, flake check green,
re-audit. Rendering is V3 -> HARDWARE-QUEUE eyeball entries.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

themes/ristretto.json

@@ -7,7 +7,7 @@
   "colors": {
     "base": "#2c2525",
     "mantle": "#251f1f",
-    "surface": "#72696a",
+    "surface": "#675e5f",
     "overlay": "#948a8b",
     "text": "#e6d9db",
     "subtext": "#e6d9db",