harden: escape every interpolation into popup innerHTML, and add default-src to both manifests (closes #307)

A hostile ERC-20's symbol() reached an innerHTML string unescaped, and neither
manifest declared default-src, so an attacker deploying a token with 1,000+
holders and airdropping one unit could render a full-viewport cross-origin
iframe over the wallet's own UI, on screens where the user types their
password.

escapeHtml is now a pure string replace over & < > " ' — the old version
round-tripped through textContent, which escapes neither quote, while already
being used inside data-copy="...". All 19 files in src/popup/views/ were
audited: beyond the reported symbol site, the explorer-supplied directionLabel
in all three transaction lists, wallet.name, addr.ensName, the blockie data:
URIs and two ad-hoc quote-only escapes were also unescaped. Explorer URLs now
go through one helper that percent-encodes the path segment.

Both manifests add default-src 'self', frame-src 'none', form-action 'none' and
base-uri 'none'. Three loosenings are pinned in tests/manifest.test.js and
justified in README.md: style-src 'unsafe-inline' (39 static style attributes;
Firefox implements neither style-src-attr nor 'unsafe-hashes'), img-src data:
(blockies), connect-src https: http: (user-configurable RPC).

Note frame-src 'none' blocks a frame loading, not the element existing, so the
zero-iframe assertion is a claim about the escaping alone; the test asserts the
element count and the literal rendered text separately, taking the count before
any click an overlay could intercept.

Verified: make check 39 suites / 811 tests, test-e2e 55/55 including the
WebAssembly-under-CSP assertion, test-e2e-firefox 8/8, zero CSP violations
asserted rather than merely unobserved. Reverting only balanceLine's
interpolation reproduces the attack as 2 iframes on the address screen.

src/popup/views/confirmTx.js

@@ -10,6 +10,7 @@ const {
     showView,
     addressTitle,
     escapeHtml,
+    displaySymbol,
     renderAddressHtml,
     attachCopyHandlers,
     goBack,
@@ -57,7 +58,7 @@ function restore() {
 
 function blockieHtml(address) {
     const src = makeBlockie(address);
-    return `<img src="${src}" width="48" height="48" style="image-rendering:pixelated;border-radius:50%;display:inline-block">`;
+    return `<img src="${escapeHtml(src)}" width="48" height="48" style="image-rendering:pixelated;border-radius:50%;display:inline-block">`;
 }
 
 function confirmAddressHtml(address, ensName, title) {
@@ -81,7 +82,11 @@ function show(txInfo) {
     feeWei = null;
 
     const isErc20 = txInfo.token !== "ETH";
-    const symbol = isErc20 ? txInfo.tokenSymbol || "?" : "ETH";
+    // The raw symbol is the price-table key; the capped one is what the
+    // screen says. Truncating before the lookup would silently drop the
+    // price of any token whose symbol is long enough to be capped.
+    const rawSymbol = isErc20 ? txInfo.tokenSymbol || "?" : "ETH";
+    const symbol = displaySymbol(rawSymbol);
 
     // Transaction type
     if (isErc20) {
@@ -123,7 +128,7 @@ function show(txInfo) {
 
     // Amount (with inline USD)
     const ethPrice = getPrice("ETH");
-    const tokenPrice = getPrice(symbol);
+    const tokenPrice = getPrice(rawSymbol);
     const amountNum = parseFloat(txInfo.amount);
     const price = isErc20 ? tokenPrice : ethPrice;
     const amountUsd = price ? amountNum * price : null;
@@ -156,7 +161,12 @@ function show(txInfo) {
         warningsEl.innerHTML = localWarnings
             .map(
                 (w) =>
-                    `<div class="border border-border border-dashed p-2 mb-1 text-xs font-bold">WARNING: ${w.message}</div>`,
+                    // Only the three hardcoded strings in
+                    // src/shared/addressWarnings.js reach this today, but
+                    // src/shared/etherscanLabels.js already builds a
+                    // `warning` out of scraped explorer markup, so this is
+                    // one wiring change away from carrying remote text.
+                    `<div class="border border-border border-dashed p-2 mb-1 text-xs font-bold">WARNING: ${escapeHtml(w.message)}</div>`,
             )
             .join("");
         warningsEl.style.visibility = "visible";
@@ -206,7 +216,7 @@ function show(txInfo) {
 // touches already occupies its space, so re-running it never moves anything.
 function renderValidation(txInfo) {
     const isErc20 = txInfo.token !== "ETH";
-    const symbol = isErc20 ? txInfo.tokenSymbol || "?" : "ETH";
+    const symbol = isErc20 ? displaySymbol(txInfo.tokenSymbol || "?") : "ETH";
 
     const { canSend, codes } = validateTransfer({
         isErc20,