feat(market): rework tab layout — responsive chart + refined portfolio + group cards

The Market tab is non-scrolling, but an oversized fixed-height chart ate ~65%
of the height and squeezed the portfolio into a cramped strip, with custom
groups rendered as tiny afterthought rows at the very bottom.

- Precompute section geometry (hero header + portfolio card height) up front and
  let the price chart ABSORB the remaining vertical space, capped at its schema
  height and floored at 130px*vs so it stays useful. The chart now shrinks to
  make room instead of dominating. Replaces the barely-used SectionBudget.
- Portfolio summary refined: fiat value stays the hero with the 24h change beside
  it and the BTC value right-aligned; DRGX balance + Z/T breakdown on the next
  row; a full-width shielded/transparent ratio bar + % label.
- Custom groups now render as a wrapping grid of mini glass cards (label + DRGX +
  fiat each), sized to the card width, instead of a cramped one-line list. A
  "GROUPS" subheader separates them from the all-funds summary. The card grows to
  fit the grid.

New i18n key portfolio_groups ("GROUPS"). Full-node + Lite build clean; ctest
1/1; hygiene clean. Rendering change — needs a screenshot check of the Market tab.

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

src/util/i18n.cpp

@@ -1119,6 +1119,7 @@ void I18n::loadBuiltinEnglish()
         strings_["market_pct_shielded"] = "%.0f%% Shielded";
         strings_["market_portfolio"] = "MY DRGX";
         strings_["portfolio_all_funds"] = "All funds";
+        strings_["portfolio_groups"] = "GROUPS";
         strings_["portfolio_manage"] = "Manage\xE2\x80\xA6";
         strings_["portfolio_manage_title"] = "Manage portfolio";
         strings_["portfolio_add_entry"] = "Add entry";