fix: a tracked token reads quantity unknown at an address no refresh has read (closes #720)

A new address, a new wallet and a network switch each leave tracked tokens
with no balance entry, so their lines read 0.0000 before any refresh had read
them.

Each of these now sets `balanceNotFetched` on the tracked tokens, and a refresh
already clears it. Their lines read `quantity unknown` until then. Addresses
that the wallet scan finds get the same. A refresh that did not read every
address the page now holds leaves the field set.

Model: opus-5-5

src/shared/chainSwitchFields.js

@@ -48,9 +48,14 @@ function applyChainSwitchFields(s, newNetworkId) {
     // It is a copy because a save writes a changed s.networkTrackedTokens whole,
     // over any list another page stored. An add or removal on the active network
     // must change only s.trackedTokens.
+    //
+    // Each token of the copy gets `balanceNotFetched`, because the balances are
+    // cleared below and no refresh has read this network's yet. Each reads
+    // `quantity unknown` until one has, not 0.0000.
     if (!s.networkTrackedTokens) s.networkTrackedTokens = {};
     s.networkTrackedTokens[s.networkId] = s.trackedTokens;
     s.trackedTokens = structuredClone(s.networkTrackedTokens[net.id] || []);
+    for (const token of s.trackedTokens) token.balanceNotFetched = true;
 
     s.networkId = net.id;
     s.rpcUrl = remembered.rpcUrl || net.defaultRpcUrl;