feat(addresses): improve address labeling and view-only handling

- Add expanded address icon picker with search, bottom-aligned actions, and improved modal sizing
- Embed a pickaxe icon font subset and wire it into typography/address icon rendering
- Track view-only shielded addresses and prevent sends from non-spendable z-addresses
- Improve address transfer dialog sizing, max amount handling, and text clipping
- Tune main header layout values in ui.toml
- Update README, codebase overview, and third-party license documentation

src/data/wallet_state.h

@@ -18,6 +18,7 @@ struct AddressInfo {
     std::string address;
     double balance = 0.0;
     std::string type;  // "shielded" or "transparent"
+    bool has_spending_key = true;  // false for view-only (imported via z_importviewingkey)
     
     // For display
     std::string label;
@@ -25,6 +26,7 @@ struct AddressInfo {
     // Derived
     bool isZAddr() const { return !address.empty() && address[0] == 'z'; }
     bool isShielded() const { return type == "shielded"; }
+    bool isSpendable() const { return has_spending_key; }
 };
 
 /**