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/tests/host_map.h

@@ -64,6 +64,7 @@
 #define SRC          (BVARS + 8)
 #define SRC_HOOK     (BVARS + 9)
 #define STORAGE_REG  (BVARS + 10)
+#define BOOT_CELLS   (BVARS + 14)               /* (BOOT): DP and LATEST as the loader left them, 2 cells */
 #define BUF0_W       (BVARS - 2 * 256)          /* the two block buffers, 256 cells each */
 #define BUF1_W       (BUF0_W + 256)
 #define QVARS        (BUF0_W - 4)               /* (Q): quit.v4, system.v4 and blocks.v4, 4 cells */
@@ -128,6 +129,7 @@ static int host_load(v4_text *tx, v4_node *n, const char *const *files, unsigned
     v4_text_constant(tx, "(W)", WVARS);
     v4_text_constant(tx, "(X)", XVARS);
     v4_text_constant(tx, "(B)", BVARS);
+    v4_text_constant(tx, "(BOOT)", BOOT_CELLS);
     v4_text_constant(tx, "SCR", SCR);
     v4_text_constant(tx, "BLK", BLK);
     v4_text_constant(tx, "(SRC)", SRC);