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/app_network.cpp

@@ -750,6 +750,19 @@ void App::refreshAddressData()
                 AddressInfo info;
                 info.address = addr.get<std::string>();
                 info.type = "shielded";
+                // Check if we have the spending key for this address
+                try {
+                    json vResult = rpc_->call("z_validateaddress", json::array({info.address}));
+                    if (vResult.is_object() && vResult.contains("ismine") && vResult["ismine"].get<bool>()) {
+                        // "ismine" means we have the spending key
+                        info.has_spending_key = true;
+                    } else {
+                        info.has_spending_key = false;
+                    }
+                } catch (...) {
+                    // If validation fails, assume spendable (safe default for older daemons)
+                    info.has_spending_key = true;
+                }
                 zAddrs.push_back(info);
             }
         } catch (const std::exception& e) {
@@ -1850,6 +1863,21 @@ void App::sendTransaction(const std::string& from, const std::string& to,
         return;
     }
     
+    // Check that we have the spending key for the from address
+    if (!from.empty() && from[0] == 'z') {
+        bool spendable = false;
+        for (const auto& addr : state_.z_addresses) {
+            if (addr.address == from) {
+                spendable = addr.has_spending_key;
+                break;
+            }
+        }
+        if (!spendable) {
+            if (callback) callback(false, "This is a view-only address (no spending key). Import the spending key to send from this address.");
+            return;
+        }
+    }
+    
     // Build recipients array
     nlohmann::json recipients = nlohmann::json::array();
     nlohmann::json recipient;