fix: the ETH line reads unknown at an address no refresh has read (closes #736)

An address's ETH balance is now null until a refresh has read it. That covers
a new address, a new wallet, addresses a wallet scan finds, and every address
after a network switch.

Its line reads `quantity unknown`, Home's balance `unknown (ETH)`, and Send
`Current balance: unknown (ETH)`. Max says the balance is unknown. Send is no
longer refused as zero. The address has no total, and DeleteAddress keeps its
warning.

A refresh also deletes `balanceNotFetched` only when it read every address in
the stored record.

Model: opus-5-5

tests/deleteAddress.test.js

@@ -33,6 +33,7 @@ const USDC = "0xa0b86991c6218b36c1d19d4a2e9eb0ce3606eb48";
 const EMPTY = { address: "0x1", balance: "0.0000", tokenBalances: [] };
 const ETH_ONLY = { address: "0x1", balance: "1.5", tokenBalances: [] };
 const DUST = { address: "0x1", balance: "0.00001", tokenBalances: [] };
+const NOT_READ = { address: "0x1", balance: null, tokenBalances: [] };
 const TOKEN_ONLY = {
     address: "0x1",
     balance: "0.0000",
@@ -106,6 +107,11 @@ describe("whether an address holds anything", () => {
         expect(addressHoldsFunds(DUST)).toBe(true);
     });
 
+    // No refresh has read it, so the address may hold funds.
+    test("an ETH balance no refresh has read counts", () => {
+        expect(addressHoldsFunds(NOT_READ)).toBe(true);
+    });
+
     test("an address holding nothing does not", () => {
         expect(addressHoldsFunds(EMPTY)).toBe(false);
         expect(addressHoldsFunds(ZERO_TOKEN)).toBe(false);
@@ -143,6 +149,13 @@ describe("the balance warning on the removal confirmation", () => {
     // The sentence must not assert an amount, because any amount it could
     // assert has been rounded: "This address holds 0.0000 ETH." is what the
     // rounded form produces for an address that holds real money.
+    test("an ETH balance no refresh has read is warned about, and reads as unknown", () => {
+        const html = balanceWarningHtml(NOT_READ);
+        expect(html).toContain("This address holds a balance");
+        expect(html).toContain("quantity unknown");
+        expect(html).not.toContain("0.0000");
+    });
+
     test("the warning sentence asserts no rounded amount", () => {
         for (const addr of [DUST, ETH_ONLY, TOKEN_ONLY]) {
             expect(balanceWarningHtml(addr)).not.toMatch(