feat(portfolio): persisted portfolio entries + pure sum helpers

Foundation for the Market tab's configurable portfolio (custom labels tied to
groups of addresses):

- Settings gains a PortfolioEntry {label, addresses[]} list, persisted in
  settings.json as a JSON array-of-objects (same mechanism as lite_servers_),
  with get/setPortfolioEntries().
- data/portfolio.h (header-only, ImGui-free): SumPortfolioBalance() sums a
  group's DRGX balance against the live per-address list (unknown addresses
  contribute 0), plus PortfolioEntryContains/Add/Remove group helpers.
- Unit-tested (testPortfolioHelpers): empty/known/unknown-address sums, and the
  add/remove/contains membership semantics.

UI (editor dialog, Market card rework, Overview right-click) comes next.
Full-node + lite build clean; ctest green.

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

src/config/settings.h

@@ -73,6 +73,13 @@ public:
         bool enabled = true;
     };
 
+    // A user-defined portfolio entry: a custom label tied to a group of wallet addresses.
+    // The Market tab's portfolio card sums these addresses' balances under the label.
+    struct PortfolioEntry {
+        std::string label;
+        std::vector<std::string> addresses;
+    };
+
     // Theme
     std::string getTheme() const { return theme_; }
     void setTheme(const std::string& theme) { theme_ = theme; }
@@ -251,6 +258,10 @@ public:
     const std::vector<LiteServerPreference>& getLiteServers() const { return lite_servers_; }
     void setLiteServers(const std::vector<LiteServerPreference>& servers) { lite_servers_ = servers; }
 
+    // User-defined portfolio entries (Market tab). "All funds" is implicit, not stored here.
+    const std::vector<PortfolioEntry>& getPortfolioEntries() const { return portfolio_entries_; }
+    void setPortfolioEntries(const std::vector<PortfolioEntry>& entries) { portfolio_entries_ = entries; }
+
     // Lite servers the user has hidden from the Network tab (kept by URL, shown via a toggle).
     const std::set<std::string>& getLiteHiddenServers() const { return lite_hidden_servers_; }
     bool isLiteServerHidden(const std::string& url) const { return lite_hidden_servers_.count(url) > 0; }
@@ -432,6 +443,8 @@ private:
     };
     std::set<std::string> lite_hidden_servers_;   // server URLs hidden from the Network tab
 
+    std::vector<PortfolioEntry> portfolio_entries_;   // Market tab custom portfolio groups
+
     bool verbose_logging_ = false;
     std::set<std::string> debug_categories_;
     bool theme_effects_enabled_ = true;