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, line and paragraph separator, and 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 +45,16 @@ 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, line and paragraph separators 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 token that reports more than 80 decimal places has no known
   scale ([#350](https://git.eeqj.de/sneak/AutistMask/issues/350)). The shared
   scale check `toDecimals()` accepted any `uint8`, but `formatUnits()` throws