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/retro-82.json

@@ -7,7 +7,7 @@
   "colors": {
     "base": "#05182e",
     "mantle": "#041427",
-    "surface": "#00172e",
+    "surface": "#0a2540",
     "overlay": "#134e5a",
     "text": "#f6dcac",
     "subtext": "#a7c9c6",