feat(v4.0.0): logging, as v3

- capsule/log.v4: the level constants LOG-ERROR .. LOG-DEBUG, LOG-LEVEL!
  and LOG-LEVEL@, LOG-ERROR" .. LOG-DEBUG" and LOG-ERROR-STR ..
  LOG-DEBUG-STR.  A message is printed if its level is at or below
  LOG-LEVEL, as v3's line -- colour, level, text -- without the time of
  day, which a node has not got.
- LOG-xxx" compiles like ." : the level, a call to (LOG"), the text.  SEE
  shows it as text.  COLD puts LOG-LEVEL back to LOG-INFO.
- tests/test_host_quit.c: ten transcripts of the v3 binary, every level
  at every setting.

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 LOG_LEVEL    (BUF0_W - 5)               /* the level at or below which a message is printed */
 #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)
@@ -130,6 +131,7 @@ static int host_load(v4_text *tx, v4_node *n, const char *const *files, unsigned
     v4_text_constant(tx, "(X)", XVARS);
     v4_text_constant(tx, "(B)", BVARS);
     v4_text_constant(tx, "(BOOT)", BOOT_CELLS);
+    v4_text_constant(tx, "(LOG-LEVEL)", LOG_LEVEL);
     v4_text_constant(tx, "SCR", SCR);
     v4_text_constant(tx, "BLK", BLK);
     v4_text_constant(tx, "(SRC)", SRC);