feat(v4): the ROM assembles the system's .f18 to the nucleus, word for word

capsules/v4/sys: the nucleus's fourteen sources as .f18 blobs (made once by
v4/tools/v4tof18.py: header becomes the ROM's directives, every other token
and line kept), the memory map as map-<width>.f18 (mkmap sys, from one
table in host_map.h that host_load reads too), and end.f18, the switch-on
state mkimage.c set in C, the image record, and start (IDLE).

test_host_rom_nucleus.c: the ROM, fed those blobs through the console,
builds RAM identical word for word to mkimage.c's, outside its own state
and the image record, and starts at (IDLE), at both widths.  The cost:
60.7 million instructions, 1.5 s on the C model.

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

capsules/v4/sys/end.f18

@@ -0,0 +1,35 @@
+\ end.f18 -- the end of the system's source: the state it is switched on in.
+\
+\ What v4/tools/mkimage.c set in C when it built the nucleus, said with the
+\ ROM's directives (MACHINE.md, the ROM's language).  RAM is all zeroes
+\ when the machine starts, so only what is not zero is stored.  Then the
+\ image record (map: (IMG)), the addresses a host needs (v4/image.h), and
+\ start: the ROM clears what it used and the node waits for a message.
+
+\ the dictionary: empty, at DBASE; the newest entry, the nucleus's last
+store DP  DBASE
+store (LATEST)  HDR-LINK
+\ the control-flow stack, the number base, the log level
+store (CFP)  CFBASE
+store BASE  10
+store (LOG-LEVEL)  2
+\ one vocabulary, FORTH, whose head cell is LATEST; new words go into it
+store CONTEXT  (LATEST)
+store CURRENT  (LATEST)
+\ the text interpreted is the terminal's
+store (SRC)  TIB
+\ what COLD comes back to, and the lowest FORGET goes: the nucleus as it is
+store (BOOT)  DBASE
+store (BOOT)+1  HDR-LINK
+store FENCE  DICT-W
+\ nothing has ended badly; nothing has been printed
+store (LINE-STATUS)  1
+store (OUT^)  (OUT)
+
+\ the image record: where the node waits, its fault table, KEY's code
+store (IMG)  &(IDLE)
+store (IMG)+1  &(FAULTS)
+store (IMG)+2  &KEY
+store (IMG)+3  &CR
+
+start (IDLE)