Light mode: darken secondary/metadata text for AA contrast

The light --muted/--faint greys were washed out: --faint #978996 was only
3.1:1 on white (failed WCAG-AA), used for metadata, star counts, the hero
pills and the footer. Darken:
- --muted #6A5965 -> #5E5159 (~7.1:1) for more presence
- --faint #978996 -> #766678 (~5.0:1, was 3.1 — now passes AA)

Both live on @btravstack/theme, so the docs sites' light secondary text
(--vp-c-text-2/-3) gets the same lift. Verified: pills 7.1:1, stars/footer
5.0:1; build green.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: btravers

packages/theme/src/tokens.css

@@ -147,8 +147,8 @@
   --border-2: rgba(26, 12, 20, 0.17);
 
   --text:  #1F0E18;
-  --muted: #6A5965;
-  --faint: #978996;
+  --muted: #5E5159;   /* ~7.1:1 on white */
+  --faint: #766678;   /* ~5.0:1 on white (was #978996, 3.1 — failed AA) */
 
   --accent:      #E0589A;   /* fill unchanged (dark ink on top) */
   --text-accent: #D6246F;   /* small labels / links — vivid raspberry, ~4.6:1 AA on white */