docs: say what a closed window does to a tx or sign approval (closes #505)

The approval port's disconnect handler leaves a transaction or signing
approval pending, and its comments said that was so the user could reopen
the toolbar popup. Those approvals open in their own window. When that
window closes, the windows.onRemoved listener rejects the approval, unless
an approved attempt is still running, in which case that attempt answers
the page. Both comments now say so. No code changed.

Model: opus-5-5

src/background/index.js

@@ -632,8 +632,9 @@ function isExtensionSender(sender) {
 // had refused.
 //
 // TX and sign approvals do not decide here. They stay pending across a
-// disconnect — the user can reopen the toolbar popup — and are rejected by the
-// windows.onRemoved listener below.
+// disconnect. When their window closes, the windows.onRemoved listener below
+// rejects them, unless an approved attempt is still running, in which case
+// that attempt answers the page.
 runtime.onConnect.addListener((port) => {
     if (port.name.startsWith("approval:")) {
         const id = port.name.split(":")[1];
@@ -661,7 +662,9 @@ runtime.onConnect.addListener((port) => {
             const approval = pendingApprovals[id];
             if (approval) {
                 if (approval.type === "tx" || approval.type === "sign") {
-                    // Keep pending — user can reopen the toolbar popup
+                    // When its window closes, windows.onRemoved rejects it,
+                    // unless an approved attempt is still running, in which
+                    // case that attempt answers the page.
                     return;
                 }
                 settleApproval(id, { approved: false, remember: false });