refactor: vendor phishing blocklist, delta-only memory model

- Vendor community-maintained phishing domain blocklist into
  src/shared/phishingBlocklist.json (bundled at build time by esbuild)
- Refactor phishingDomains.js: build vendored Sets at module load,
  fetch live list periodically, keep only delta (new entries not in
  vendored) in memory for small runtime footprint
- Domain checker checks delta first (fresh scam sites), then vendored
- Persist delta to localStorage if under 256 KiB
- Load delta from localStorage on startup for instant coverage
- Add startPeriodicRefresh() with 24h setInterval in background script
- Remove dead code: popup's local isPhishingDomain() re-check was inert
  (popup never called updatePhishingList so its blacklistSet was always
  empty); now relies solely on background's authoritative flag
- Remove all competitor name mentions from UI warning text and comments
- Update README: document phishing domain protection architecture,
  update external services list
- Update tests: cover vendored blocklist loading, delta computation,
  localStorage persistence, delta+vendored interaction

Closes #114

README.md

@@ -15,10 +15,12 @@ Hence, a minimally viable ERC20 browser wallet/signer that works cross-platform.
 Everything you need, nothing you don't. We import as few libraries as possible,
 don't implement any crypto, and don't send user-specific data anywhere but a
 (user-configurable) Ethereum RPC endpoint (which defaults to a public node). The
-extension contacts exactly three external services: the configured RPC node for
+extension contacts three user-configurable services: the configured RPC node for
 blockchain interactions, a public CoinDesk API (no API key) for realtime price
 information, and a Blockscout block-explorer API for transaction history and
-token balances. All three endpoints are user-configurable.
+token balances. It also fetches a community-maintained phishing domain blocklist
+periodically and performs best-effort Etherscan address label lookups during
+transaction confirmation.
 
 In the extension is a hardcoded list of the top ERC20 contract addresses. You
 can add any ERC20 contract by contract address if you wish, but the hardcoded
@@ -576,14 +578,25 @@ What the extension does NOT do:
 
 - No analytics or telemetry services
 - No token list APIs (user adds tokens manually by contract address)
-- No phishing/blocklist APIs
 - No Infura/Alchemy dependency (any JSON-RPC endpoint works)
 - No backend servers operated by the developer
 
-These three services (RPC endpoint, CoinDesk price API, and Blockscout API) are
-the only external services. All three endpoints are user-configurable. Users who
-want maximum privacy can point the RPC and Blockscout URLs at their own
-self-hosted instances (price fetching can be disabled in a future version).
+In addition to the three user-configurable services above (RPC endpoint,
+CoinDesk price API, and Blockscout API), AutistMask also contacts:
+
+- **Phishing domain blocklist**: A community-maintained phishing domain
+  blocklist is vendored into the extension at build time. At runtime, the
+  extension fetches the live list once every 24 hours to detect newly added
+  domains. Only the delta (domains not already in the vendored list) is kept in
+  memory, keeping runtime memory usage small. The delta is persisted to
+  localStorage if it is under 256 KiB.
+- **Etherscan address labels**: When confirming a transaction, the extension
+  performs a best-effort lookup of the recipient address on Etherscan to check
+  for phishing/scam labels. This is a direct page fetch with no API key; the
+  user's browser makes the request.
+
+Users who want maximum privacy can point the RPC and Blockscout URLs at their
+own self-hosted instances (price fetching can be disabled in a future version).
 
 ### Dependencies
 
@@ -773,6 +786,22 @@ indexes it as a real token transfer.
   designed as a sharp tool — users who understand the risks can configure the
   wallet to show everything unfiltered, unix-style.
 
+#### Phishing Domain Protection
+
+AutistMask protects users from known phishing sites when they connect their
+wallet or approve transactions/signatures. A community-maintained domain
+blocklist is vendored into the extension at build time, providing immediate
+protection without any network requests. At runtime, the extension fetches the
+live list once every 24 hours and keeps only the delta (newly added domains not
+in the vendored list) in memory. This architecture keeps runtime memory usage
+small while ensuring fresh coverage of new phishing domains.
+
+When a dApp on a blocklisted domain requests a wallet connection, transaction
+approval, or signature, the approval popup displays a prominent red warning
+banner alerting the user. The domain checker matches exact hostnames and all
+parent domains (subdomain matching), with whitelist overrides for legitimate
+sites that share a parent domain with a blocklisted entry.
+
 #### Transaction Decoding
 
 When a dApp asks the user to approve a transaction, AutistMask attempts to