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 for history
and token lookups, and each recipient to Etherscan for its label. Two settings,
"Use Blockscout" and "Check recipients on Etherscan", now gate those requests
where they are made. Both are off in a new profile and offered unticked on
Welcome and in Settings. While one is off, the screens that relied on it say so
in a plain line naming the setting; after either changes in Settings, Back
draws the screen it lands on again. README and the user guide say what is
contacted by default and what each setting adds.

Model: opus-5-5

docs/README.md

@@ -57,11 +57,12 @@ analytics, use a portfolio tracker. The wallet is not the place for any of that.
 
 - **No NFT galleries or portfolio views.** This is a wallet, not a dashboard.
 
-- **No third-party token list APIs.** Token balances come from the same block
-  explorer you configure for transaction history, and the extension ships its
-  own hardcoded list of top ERC-20 contract addresses for symbol-spoofing
-  detection. Any token you want tracked across all your addresses, you add
-  yourself by contract address.
+- **No third-party token list APIs.** The balances of the tokens you track are
+  read from your RPC endpoint; while you have "Use Blockscout" on, the others
+  come from the same block explorer you configure for transaction history. The
+  extension ships its own hardcoded list of top ERC-20 contract addresses for
+  symbol-spoofing detection. Any token you want tracked across all your
+  addresses, you add yourself by contract address.
 
 - **No backend servers operated by the developer.** Nothing is sent to any
   server run by AutistMask. Every network destination is listed below.
@@ -69,8 +70,11 @@ analytics, use a portfolio tracker. The wallet is not the place for any of that.
 ## How It Works
 
 AutistMask is a browser extension that runs entirely in your browser. It does
-not have a backend server. It communicates with five external destinations:
-three you configure yourself, and two fixed ones used for scam detection.
+not have a backend server. Out of the box it sends your data only to the
+Ethereum RPC endpoint, and asks the CoinDesk price API for prices with nothing
+but token symbols. Blockscout and Etherscan are sent none of your data until you
+turn on "Use Blockscout" or "Check recipients on Etherscan", on the Welcome
+screen or later in Settings. Both are off in a new install.
 
 ### External Services
 
@@ -96,16 +100,23 @@ addresses are necessarily visible to the RPC provider when querying balances.
 **Blockscout API** (default: `eth.blockscout.com/api/v2`;
 `eth-sepolia.blockscout.com/api/v2` on Sepolia)
 
-Used to fetch token balances and transaction history. Blockscout is an
-open-source blockchain explorer. AutistMask queries it for your ERC-20 token
-balances (including the holder counts used for spam filtering) and your recent
-transactions and token transfers. You can change this in Settings to a
-self-hosted Blockscout instance.
+Off until you turn on "Use Blockscout". Used to fetch transaction history, the
+balances of the tokens you have not tracked, and the details of a transaction
+you open. Blockscout is an open-source blockchain explorer. AutistMask queries
+it for your ERC-20 token balances (including the holder counts used for spam
+filtering), your recent transactions and token transfers, and the block, fees
+and calldata of a transaction you open. You can change this in Settings to a
+self-hosted Blockscout instance. While it is off, the screens that would show
+history say so, and only the tokens you track are listed.
 
-When it is contacted: on every balance refresh, and whenever a screen showing
-transaction history is opened.
+When it is contacted: only while "Use Blockscout" is on, on every balance
+refresh, whenever a screen showing transaction history is opened, and when you
+open a transaction.
 
-What gets sent: your Ethereum addresses (to look up balances and transactions).
+What gets sent: your Ethereum addresses (to look up balances and transactions)
+and the hash of each transaction you open. Pressing "Save" beside the Blockscout
+URL in Settings checks that URL by asking it for `/stats`, which sends none of
+your data, whether or not the setting is on.
 
 **CoinDesk CADLI price API** (`data-api.coindesk.com`)
 
@@ -122,13 +133,16 @@ address.
 
 **Etherscan address labels** (`etherscan.io`; `sepolia.etherscan.io` on Sepolia)
 
-When you review a send, AutistMask fetches the recipient's public Etherscan
-address page and looks for a "Fake_Phishing"/"Phish/Hack" label or a scam
-warning, and shows a red warning if it finds one. This is a plain page fetch
-with no API key, made by your browser. It is best-effort: if it fails, it is
-silently ignored. This endpoint is not user-configurable.
+Off until you turn on "Check recipients on Etherscan". When you review a send,
+AutistMask fetches the recipient's public Etherscan address page and looks for a
+"Fake_Phishing"/"Phish/Hack" label or a scam warning, and shows a red warning if
+it finds one. This is a plain page fetch with no API key, made by your browser.
+It is best-effort: if it fails, it is silently ignored. This endpoint is not
+user-configurable. While it is off, the confirmation screen says that no
+Etherscan check was made.
 
-When it is contacted: each time you reach the send confirmation screen.
+When it is contacted: only while "Check recipients on Etherscan" is on, each
+time you reach the send confirmation screen.
 
 What gets sent: the recipient address you are about to send to, and your IP
 address. Your own addresses are not sent.
@@ -185,6 +199,9 @@ password.
 
 1. Click the AutistMask icon in your browser toolbar.
 2. Click "Add wallet" (on first use), or open Settings and click "+ Add wallet".
+   On first use the same screen offers "Use Blockscout" and "Check recipients on
+   Etherscan", both off; tick either if you want what it does (see External
+   Services). You can change both later in Settings.
 3. On the "From Phrase" tab, click the die button to generate a random 12-word
    recovery phrase.
 4. **Write down the recovery phrase and store it safely.** Anyone with these
@@ -220,10 +237,11 @@ always produce the same sequence of addresses.
 
 ### Adding ERC-20 Tokens
 
-Tokens you hold show up automatically only if they are in the extension's
-bundled list of well-known tokens or have at least 1,000 holders; everything
-else is treated as spam and hidden. To track a token explicitly (which also
-shows it at zero balance), add it by contract address:
+Tokens you hold show up automatically only while "Use Blockscout" is on, and
+then only if they are in the extension's bundled list of well-known tokens or
+have at least 1,000 holders; everything else is treated as spam and hidden. To
+track a token explicitly (which also shows it at zero balance, and shows it
+whether or not "Use Blockscout" is on), add it by contract address:
 
 1. Go to an address detail view (click `[info]` on any address).
 2. Click "+ Token".
@@ -389,8 +407,10 @@ Click the gear icon on the home screen to access settings:
   that network's defaults if you have not used it before.
 - **Ethereum RPC**: Change the Ethereum node endpoint. Default is a public RPC.
   You can use your own node for maximum privacy.
-- **Blockscout API**: Change the Blockscout instance used for token balances and
-  transaction history. You can use a self-hosted instance.
+- **Blockscout API**: "Use Blockscout", off until you tick it, and the
+  Blockscout instance used for transaction history, the tokens you have not
+  tracked and transaction details. You can use a self-hosted instance.
+- **Etherscan**: "Check recipients on Etherscan", off until you tick it.
 - **Token Spam Protection**: Toggle individual scam filters and set the dust
   transaction threshold.
 - **Allowed Sites / Denied Sites**: View and manage web3 site permissions.