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/vantablack.json

@@ -48,7 +48,7 @@
     "#9b9b9b",
     "#b0b0b0",
     "#ececec",
-    "#fdfdfd",
+    "#666666",
     "#a4a4a4",
     "#b6b6b6",
     "#cecece",