harden: warn for token-permission typed data and show the primary type ethers signs (closes #400)

The typed-data screen listed a Permit or Permit2 signature as plain
key/value lines, exactly like a sign-in message. For EIP-2612's Permit and
Permit2's signature types it now shows a red warning naming the spender and
each token and amount, Unlimited for the field's largest value.

The screen printed the page's primaryType, but ethers signs the type it
derives from types. It now shows the derived type, and typed data whose
stated type is missing or differs is refused: error line, Sign disabled,
and checked again where signing starts.

Deviation: the warning names no deadline or expiry; see the issue.
Judgement call: DAI's older permit and Permit2's batch and witness transfer
types are recognised too.

Model: opus-5-5

README.md

@@ -911,9 +911,10 @@ approximation but a different number — 1,000 units of a 6-decimal token
 formatted at 18 decimals reads `0.000000001` — on the screen whose only job is
 to state what is being authorized. Both amount paths of that screen take this
 rule: the ERC-20 `transfer`/`approve` line (`src/popup/views/approval.js`) and
-the swap's `Amount` and `Min. received` lines (`src/shared/uniswap.js`). An
-unbounded allowance or permit needs no scale to describe and is still shown as
-`Unlimited`.
+the swap's `Amount` and `Min. received` lines (`src/shared/uniswap.js`). The
+token permission warning on the signature screen takes the same rule for its
+amounts. An unbounded allowance or permit needs no scale to describe and is
+still shown as `Unlimited`.
 
 The rule holds only if nothing invents a scale UPSTREAM of it. Those three
 sources are read as authoritative, so a value written into one of them cannot be
@@ -1801,10 +1802,21 @@ view would leave a wallet one click from deletion.
     - Type: "Personal message" or "Typed data (EIP-712)"
     - From: color dot + full address + etherscan link
     - Message: decoded UTF-8 text (personal_sign) or formatted domain/type/
-      message fields (EIP-712 typed data)
+      message fields (EIP-712 typed data). The primary type shown is the one
+      ethers signs, derived from the typed data's `types`, not the type the site
+      states.
+    - Token permission warning, at the top of the message (typed data whose
+      primary type is EIP-2612's `Permit` or one of Permit2's signature types):
+      "⚠️ TOKEN PERMISSION: Signing this lets the spender below take the tokens
+      listed here from your address, without asking you again.", then the
+      spender's full address and, for each token, its symbol, full address and
+      amount (`Unlimited` for the largest amount the field holds)
     - Password input and an error line
     - "Sign" / "Reject" buttons
 - **Transitions**:
+    - Typed data that states no primary type, or one other than the type it
+      would be signed as, or that cannot be read → shown with the error line
+      saying so and "Sign" disabled; only "Reject" remains
     - "Sign" (correct password) → signs locally → closes popup (returns
       signature)
     - "Sign" (wrong password, or a signing failure) → error line, no screen