docs(types): the empty-message fallback pin names the name it reads, not "prose"

The by-rule census caught one more carrier of the "always prose" half of the
claim, in a title no spelling-census would have matched: "answers prose for a
declared envelope whose own message is empty". Measured false in general — a
declared envelope whose `message` AND `name` are both empty answers '' — and it
contradicted the fallback sentence corrected in the previous commit. True of its
own pin, which reads `name` = 'Error'; the title now says that.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01XTBcV7zZHmokdyQgXjbyEU

Author: claude

packages/types/src/driver-error-classification.operator-text.test.ts

@@ -150,7 +150,7 @@ describe('[#16657] operatorFacingErrorText — the fallback channel when no caus
         expect(operatorFacingErrorText({})).toBe('[object Object]');
     });
 
-    it('answers prose for a declared envelope whose own message is empty', () => {
+    it('falls back to the `name` of a declared envelope whose own message is empty', () => {
         const empty = rawStatementFault(undefined, '');
         expect(operatorFacingErrorText(empty)).toBe('Error');
     });