feat(market): 2-cell min group height; declutter + polish the price chart

- Portfolio group minimum height is now 2 cells (was 3). Added a 2-cell card tier
  that also drops the sparkline (not just the footer) so a ~58px card keeps the
  header + hero value legible.
- Price chart: stop drawing a dot on every point — for a dense historical series
  (>40 points) just the clean line + fill, and always mark the latest point
  (current price) with a dot + ring.
- Y-axis labels use the shared adaptive price formatter (e.g. $0.0143) instead of
  a fixed 6 decimals, so they're cleaner and narrower.

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

src/config/settings.h

@@ -97,7 +97,7 @@ public:
         int gridCol = -1;
         int gridRow = -1;
         int gridW = 6;
-        int gridH = 3;                 // minimum group height (cells); card design adapts below ~4
+        int gridH = 3;                 // default group height (cells); minimum is 2, card design adapts
     };
 
     // Theme