harden: show a personal message's hex and its text in byte order, hidden characters marked (closes #403)

The signature screen showed only the text a personal message decodes
to, with bidirectional, right-to-left and zero-width characters acting
on it, so a site could make the message read differently from the
bytes that are signed, and a message that was not hex was decoded into
NUL characters. The screen now shows the hex as "Raw data" alongside
the text, lays the text out left to right in byte order, and shows
each control character and each character that paints nothing (the set
src/shared/symbolSpoof.js already strips) as a U+XXXX mark. A message
is hex when getBytes, which signing uses, reads it; one that is not
cannot be signed, so it is shown as plain text with "Sign" disabled.

Model: opus-5-5

TODO.md

@@ -45,6 +45,17 @@ but the review is broader than any of them.
 
 # Completed Steps
 
+- 2026-10-04: The signature screen shows a personal message as the bytes that
+  are signed ([#403](https://git.eeqj.de/sneak/AutistMask/issues/403)). It
+  showed only the decoded text, with bidirectional and zero-width characters
+  acting on it, so a site could make the message read differently from what is
+  signed, and a message that was not hex was shown as NUL characters. The hex is
+  now shown as "Raw data" alongside the decoded text, the text is laid out left
+  to right in byte order, control characters and characters that paint nothing
+  are shown as `U+XXXX` marks, and a message that is not hex by the rule signing
+  reads it with is shown as plain text with "Sign" disabled, since such a
+  message has no bytes to sign.
+
 - 2026-10-04: A site has at most one connection prompt and one signature prompt
   open at a time ([#405](https://git.eeqj.de/sneak/AutistMask/issues/405)). Each
   `eth_requestAccounts` or `personal_sign` call opened another approval window,