harden: bound the total network fee by gasLimit × fee, on both send paths (closes #399)

The two per-field ceilings in approvalVerify.js were checked independently,
but the fee a validator is paid is gasLimit × fee per gas: a gas limit and a
fee each under their own ceiling still multiply to thousands of ETH, which a
gas-consuming contract really collects. assertWithinCeilings now also bounds
that product against MAX_TOTAL_FEE (1 ETH), so both callers — populating the
dApp transaction and verifying the signed artifact — refuse it with a full
sentence naming the fee and the limit.

The wallet's own send in confirmTx.js pinned no fee fields, so ethers filled
them from the node with no bound; it now populates the transaction and runs the
same check before signing, showing the same error in the confirmation screen's
reserved errors box so nothing on screen moves.

Model: opus-4-8

TODO.md

@@ -45,6 +45,28 @@ but the review is broader than any of them.
 
 # Completed Steps
 
+- 2026-09-21: The network fee a transaction can commit is bounded by the product
+  of the gas limit and the fee per gas, not by each field alone, and the
+  wallet's own send is bounded the same way
+  ([#399](https://git.eeqj.de/sneak/AutistMask/issues/399)). The two per-field
+  ceilings in `src/shared/approvalVerify.js` were checked independently, so a
+  gas limit and a fee that were each under their own ceiling still multiplied to
+  thousands of ETH — a fee a gas-consuming contract really collects — while the
+  comment claimed the ceiling caught exactly that. `assertWithinCeilings` now
+  also refuses a transaction whose gas limit times its fee per gas
+  (`maxFeePerGas` for a type-2 transaction, `gasPrice` for a legacy or type-1
+  one) exceeds `MAX_TOTAL_FEE`, a new constant of 1 ETH beside the existing
+  ceilings, so both callers — where the dApp transaction is populated and where
+  the signed artifact is verified — reject it with a full sentence naming the
+  fee and the limit. The wallet's own send in `src/popup/views/confirmTx.js`
+  pinned no fee fields, so ethers filled them from whatever the configured node
+  answered with nothing bounding them; it now populates the transaction and runs
+  the same check before signing, showing the same error in the confirmation
+  screen's reserved errors box so nothing on screen moves. Deliberately out of
+  scope: comparing a supplied fee against the node's own suggested fee, which
+  the absolute bound already makes unnecessary for the balance-draining case. 1
+  ETH is a plain constant, one line to change; the owner may prefer another
+  figure.
 - 2026-09-21: The test recovery phrase no longer survives in a release bundle,
   and the committed-key guard matches by content
   ([#351](https://git.eeqj.de/sneak/AutistMask/issues/351)). `DEBUG_MNEMONIC` in