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/ethereal.json

@@ -7,11 +7,11 @@
   "colors": {
     "base": "#060B1E",
     "mantle": "#05091a",
-    "surface": "#060B1E",
+    "surface": "#0e1836",
     "overlay": "#6d7db6",
     "text": "#ffcead",
     "subtext": "#F99957",
-    "muted": "#6d7db6",
+    "muted": "#5568a0",
     "accent": "#7d82d9",
     "accentAlt": "#c89dc1",
     "good": "#92a593",