diag(auth): always show raw signData error, drop false-matching cancel heuristic
The cancel/reject heuristic matched any wallet error message containing "user" (etc.) and rewrote it to "Signing cancelled", which hid the real UTXOS signData failure even after we started surfacing it. Show the raw provider message verbatim so the true cause is visible. Co-Authored-By: Claude Fable 5 <[email protected]>