feat(v4): the machine boots from its ROM; the prebuilt nucleus is gone

The host node starts in its ROM (entry 12), and the boot feeds it the
system's source through the console: capsules/v4/sys/map-64.f18, the
fourteen .f18 blobs and end.f18, each found, hash-checked and
signature-checked as any capsule, then EOT.  The ROM assembles the system
and starts it at (IDLE); the host reads the image record
(v4_image_from_node) for what only the assembled system knows.  A ROM
error is reported with its blob, line and meaning, then PARITY:FAIL.

Deleted: v4/tools/mkimage.c, capsules/v4/nucleus-64.f18, v4/capsule/*.v4,
v4/tools/v4tof18.py.  The .f18 files are the source now.

- text.c speaks the rest of the ROM's language (set, here, store, start;
  v4_text_value, v4_text_start), so the oracle reads the same source:
  test_host_rom_nucleus compares the ROM against text.c on the .f18 files,
  word for word, image record included.  Host tests load the .f18 files.
- mkmap image writes v4_map_image (the map's description of the system);
  hosted and the kernel link the ROM and the map instead of v4_image_64.c.
- Hera (Captain Bob's ruling, option 1): births stream the system the ROM
  assembled, as assembled code; hera.4th is unchanged.
  test_host_unit's host builds the system with the ROM.
- New parity lines: PARITY:V4_F18 per blob, PARITY:V4_ROM words=2049
  rom_hash=0xa6c792b5821010b7 instructions=60725216.

Acceptance: amd64, aarch64, riscv64 boot to ok> with PARITY:V4_POST
tests=538 pass=538 fail=0, POST: PASSED, and PARITY:V4_SYSTEM
word_count=317 dict_hash=0xe5a57f3eb72ff94a on all three -- the same hash
as the prebuilt nucleus gave.  make -C v4 test test-32 hosted-check: all
pass.  Logs: logs/20261015-141648, -141938, -142350.

Startup cost under QEMU TCG, the ROM's assembly (last V4_F18 line to
V4_ROM): amd64 26.7 s of 132 s to ok>; aarch64 41.0 s of 195 s; riscv64
20.5 s of 101 s.  Hosted native: +0.85 s.

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

capsules/v4/sys/quit.f18

@@ -1,4 +1,4 @@
-\ quit.v4 -- a line of text, interpreted; how it ends; and the words that
+\ quit.f18 -- a line of text, interpreted; how it ends; and the words that
 \ print text written in the source.
 \
 \ DECOMPOSITION.md 5.15 and 5.10: QUIT ABORT ABORT" (ABORT") ." (.").  Part of
@@ -32,10 +32,10 @@
 \
 \ Constants the loader supplies:
 \   (LINE-STATUS)   word address of the variable: how the last text ended
-\   (MSG) (REPLY) (ME) (OUT) (OUT^)   see core.v4, "what a node prints"
+\   (MSG) (REPLY) (ME) (OUT) (OUT^)   see core.f18, "what a node prints"
 \   (PORT)  word address of the node's port 0
-\   (Q)     word address of four cells of scratch, which system.v4 and
-\           blocks.v4 use too
+\   (Q)     word address of four cells of scratch, which system.f18 and
+\           blocks.f18 use too
 \   DSTACK-DEPTH RSTACK-DEPTH   word addresses of the stack registers
 
 \ ( -- )   empty the return stack.  `a` is only something to store: any
@@ -356,7 +356,7 @@ set HDR-NFA here  ", SEND-ON  #, 0  #, HDR-NFA  #, HDR-LINK  set HDR-LINK here
 \ WHAT HAS COME ALREADY is on the wires and is found the first time
 \ through: the node looks before it sleeps.  A message it left on a wire
 \ does not keep it awake.
-\ The stack what it does needs is tried first, (ROOM), core.v4: text that
+\ The stack what it does needs is tried first, (ROOM), core.f18: text that
 \ has left too little ends "Stack overflow" with nothing taken off a wire.
 set HDR-NFA here  ", AWAIT  #, 0  #, HDR-NFA  #, HDR-LINK  set HDR-LINK here  
 : AWAIT
@@ -399,7 +399,7 @@ set HDR-NFA here  ", PORT!  #, 0  #, HDR-NFA  #, HDR-LINK  set HDR-LINK here
 
 \ ( -- )   WHAT IS IN THE DICTIONARY NOW IS THE SYSTEM: COLD comes back to
 \ it and FORGET will not go below it.  Whoever has loaded a node's capsules
-\ has it do this (system.v4, (BOOT) and FENCE).
+\ has it do this (system.f18, (BOOT) and FENCE).
 set HDR-NFA here  ", (SEAL)  #, 0  #, HDR-NFA  #, HDR-LINK  set HDR-LINK here  
 : (SEAL)
   DP a! @  (BOOT) a! !
@@ -411,7 +411,7 @@ set HDR-NFA here  ", (SEAL)  #, 0  #, HDR-NFA  #, HDR-LINK  set HDR-LINK here
 \ NODE-ERROR, by name: how a definition written in FORTH raises an error.
 \ A store of a code that is not zero is the trap of D-18 -- the word goes no
 \ further, the message for the code is printed (-1: the word has printed
-\ its own) and the line ends with ERROR.  The codes are listed in core.v4.
+\ its own) and the line ends with ERROR.  The codes are listed in core.f18.
 set HDR-NFA here  ", NODE-ERROR  #, 8  #, HDR-NFA  #, HDR-LINK  set HDR-LINK here  : NODE-ERROR'   NODE-ERROR ;
 set HDR-NFA here  ", (ME)  #, 8  #, HDR-NFA  #, HDR-LINK  set HDR-LINK here  : (ME)'       (ME) ;
 set HDR-NFA here  ", (CONSOLE)  #, 8  #, HDR-NFA  #, HDR-LINK  set HDR-LINK here  : (CONSOLE)'  (CONSOLE) ;
@@ -453,7 +453,7 @@ set HDR-NFA here  ", ABORT  #, 0  #, HDR-NFA  #, HDR-LINK  set HDR-LINK here
   2 jump (DONE)
 
 \ A word has stored an error code in NODE-ERROR (D-18; the codes are listed
-\ in core.v4).  Print its message -- a negative code means the word printed
+\ in core.f18).  Print its message -- a negative code means the word printed
 \ its own -- and end the line with ERROR.  The return stack has been
 \ emptied; the data stack is as the word left it.
 \ (QUIET) is 1 while the node is doing something that is no text's doing:
@@ -508,7 +508,7 @@ set HDR-NFA here  ", ABORT  #, 0  #, HDR-NFA  #, HDR-LINK  set HDR-LINK here
 \ The three run-time words have names, as v3's have, so that SEE can tell a
 \ string in a definition from code; they cannot be used from the prompt.
 \ ." and ABORT" take the text up to the next " , which may be none at all
-\ (input.v4's (PARSE)); with no closing " it is the rest of the line.  Inside a definition they lay
+\ (input.f18's (PARSE)); with no closing " it is the rest of the line.  Inside a definition they lay
 \ down a call to their run-time word and, after it, the text as a counted
 \ string: the count byte and the characters, four to a cell, the last cell
 \ filled with zeros.  The run-time word finds the string by the return