feat(v4.0.0): the editor, redone in FORTH; COLD WARM PAGE VERSION DEFER

- capsule/editor.fth: the block editor as FORTH source, which the node
  compiles itself.  It is a vocabulary, EDITOR, used at the ordinary
  prompt: n EDIT, then L N B T P E D S H R I WIPE DONE.  v3's EDIT, a
  shell of its own, is not carried over (ruled 2026-10-05); v3's L S and
  SHOW are kept in FORTH as they were, with COPY.
- system.v4: COLD (the system as the loader left it), WARM, PAGE,
  VERSION, 79-STANDARD (FORTH-79: silent), and DEFER IS DEFER@ as v3.
- input.v4: where words are split at blanks a zero byte reads as a blank,
  so a block never written, or filled a line at a time, loads cleanly.
- tests/test_host_quit.c: the editor's source fed to the prompt line by
  line, every command on empty and full screens, what reaches storage;
  the system words; deferred words.

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

v4/capsule/core.v4

@@ -17,6 +17,7 @@
 \    9 Shift count out of range      10 Protected word
 \   11 Division by zero (Q./)        12 Argument out of range
 \   13 Block out of range            14 No block is being loaded
+\   15 Deferred word not set
 \   -1 the word has printed its own message
 
 macro SWAP   over push push drop pop pop   endmacro