fix(themes): default light secondary indigo→teal for visible gradients

Light-mode `secondary` was `blue` (hue ~260, almost identical to the
`indigo` primary at hue ~277). Result: every primary→secondary
gradient in light mode read as a flat solid colour — Pro pricing tier
border, "Most popular" badge, Pro CTA, hero highlight (when not in
forced-dark sections), stats numbers, comparison-table accents all
lost their gradient direction.

Switch light secondary to `teal` (hue ~182). Dark mode already used
teal, so this unifies the brand pairing across modes. Visible gradient
direction restored everywhere primary→secondary is used.

No block changes needed — the fix lives in the theme palette where
similar brand decisions belong, not as workarounds in individual
blocks.

modules/blox/data/themes/default.yaml

@@ -14,7 +14,10 @@ hugoblox:
   light:
     colors:
       primary: "indigo"
-      secondary: "blue"
+      # `teal` (not `blue`) to give primary→secondary gradients visible direction
+      # in light mode — `indigo` and `blue` are nearly identical hues. Matches the
+      # dark mode pairing's `teal` so the brand reads consistently across modes.
+      secondary: "teal"
     surfaces:
       background: "#ffffff"
       foreground: "#111827"