feat(v4.0.0): every error is raised and ends the line (D-18)

Ruled 2026-10-04: guard all errors.  The errors that set NODE-ERROR and
let the line run on now stop it at once, with a message.

- A store of a non-zero code to NODE-ERROR is a trap, a sixth kind of
  fault: nothing after it executes, the return stack is emptied, and the
  data stack is left as the word left it.  Not attached, NODE-ERROR is
  plain memory, as the tests below the prompt use it.
- The capsule's words store a code where they stored -1, and the prompt's
  (RAISED) prints its message: Negative count, Not a number, Number too
  long, Not a character, Dictionary full, Name missing, Control structure
  mismatch, Control structures too deep.
- ' and COMPILE and [COMPILE] of a word that is not there say
  UNKNOWN WORD: 'xxx', as the interpreter does.
- tests: the trap in test_exec.c; every message from the prompt, with the
  rest of the line not run and the stack kept, in test_host_quit.c.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

v4/capsule/input.v4

@@ -183,7 +183,7 @@ header CONVERT
 header NUMBER
 : NUMBER
   (NUMBER?) if BAD  drop ;
-  BAD: drop  NODE-ERROR b! -1 !b ;
+  BAD: drop  NODE-ERROR b! 2 !b ;
 
 \ ---- comments (5.15) -------------------------------------------------------
 \ PAREN skips to the closing parenthesis; BACKSLASH skips the rest of the line.