fix: Blockscout and Etherscan lookups are off until the user turns them on (closes #668)

Out of the box the wallet sent the user's addresses to Blockscout and each recipient's address to Etherscan. Two settings, "Use Blockscout" and "Check recipients on Etherscan", now gate every request that sends the user's data to those services. Both start off and are offered unticked on Welcome and in Settings. Each request reads its setting from storage before it asks. An answer that lands after the setting went off is dropped. While a setting is off, the screens that rely on it say so. ENS lookups ask only the RPC endpoint, so a name resolved off-chain does not resolve.

RULES.md's External Communication item is now out of date. Its new wording will be proposed on #211 once this lands.

Model: opus-5-5 (implementation, summary); fable-5-1 (prose)

src/shared/etherscanLabels.js

@@ -3,6 +3,7 @@
 // This is a best-effort enrichment: network failures return null silently.
 
 const { networkByChainId } = require("./networks");
+const { storedSettingIsOn } = require("./storedSettings");
 
 // Patterns in the page title that indicate a flagged address.
 // Title format: "Fake_Phishing184810 | Address: 0x... | Etherscan"
@@ -78,12 +79,19 @@ function parseEtherscanPage(html) {
  * when it is omitted: etherscan.io on mainnet, sepolia.etherscan.io on
  * Sepolia.
  *
+ * While the stored "Check recipients on Etherscan" is off, Etherscan is not
+ * asked. An answer that lands after the setting went off is dropped
+ * (src/shared/storedSettings.js). Either way the answer is null.
+ *
  * @param {string} address - Ethereum address to check.
  * @param {string} [chainId] - Chain id of the network to look it up on.
  * @returns {Promise<{type: string, message: string, severity: string}|null>}
  */
 async function checkEtherscanLabel(address, chainId) {
     try {
+        if (!(await storedSettingIsOn("checkRecipientsOnEtherscan"))) {
+            return null;
+        }
         // Lazy require to avoid pulling in chrome.storage at module scope
         // (which breaks unit tests that only exercise parseEtherscanPage).
         const { currentNetwork } = require("./state");
@@ -94,6 +102,9 @@ async function checkEtherscanLabel(address, chainId) {
         });
         if (!resp.ok) return null;
         const html = await resp.text();
+        if (!(await storedSettingIsOn("checkRecipientsOnEtherscan"))) {
+            return null;
+        }
         const result = parseEtherscanPage(html);
         if (result.isPhishing) {
             return {