fix(themes): fidelity hierarchy nits + #52 residual ANSI (#67, #68)

#67 hierarchy: nord subtext dimmer than text; tokyo-night btop Night
blues; ethereal surface raise + muted darker than overlay; retro-82
surface raised; ristretto subtext distinct + btop main_bg align;
flexoki-light distinct bright-black; gruvbox overlay/subtext ladder
(no rename).

#68 residual ANSI: vantablack ansi[8]=muted; osaka-jade ansi[3]=warn.

Verified: python3 tools/check-theme-contrast.py themes/ → 24×7 all pass.

themes/ristretto.json

@@ -10,7 +10,7 @@
     "surface": "#675e5f",
     "overlay": "#948a8b",
     "text": "#e6d9db",
-    "subtext": "#e6d9db",
+    "subtext": "#c3b7b8",
     "muted": "#948a8b",
     "accent": "#f38d70",
     "accentAlt": "#a8a9eb",