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/core.f18

@@ -1,5 +1,5 @@
 set HDR-LINK 0  \ the newest dictionary entry: none yet
-\ core.v4 -- the core words the host-node capsules rest on.
+\ core.f18 -- the core words the host-node capsules rest on.
 \
 \ Each is the definition DECOMPOSITION.md gives and the golden-model tests
 \ execute (test_foundation.c, test_strings.c, test_terminal.c, test_pictured.c),
@@ -13,7 +13,7 @@ set HDR-LINK 0  \ the newest dictionary entry: none yet
 \ ERRORS (D-18).  A word that finds an error takes its arguments off the stack
 \ and stores a code in NODE-ERROR.  On a node with a prompt that store is a
 \ trap: the word goes no further, and the prompt prints the message for the
-\ code and ERROR (quit.v4, (RAISED)).  The codes:
+\ code and ERROR (quit.f18, (RAISED)).  The codes:
 \    1 Negative count        2 Not a number        3 Number too long
 \    4 Not a character       5 Dictionary full     6 Name missing
 \    7 Control structure mismatch     8 Control structures too deep
@@ -110,7 +110,7 @@ set HDR-NFA here  ", CMOVE  #, 0  #, HDR-NFA  #, HDR-LINK  set HDR-LINK here
 \ is the port it came on, by its number; (ME) is this node's number.
 \
 \ Characters are kept in (OUT), 256 of them, a character to a cell, and sent
-\ when it is full and when the text has been done with (quit.v4).  (OUT^)
+\ when it is full and when the text has been done with (quit.f18).  (OUT^)
 \ is where the next goes.
 \
 \ THE STACK.  What prints may be run with the data stack all but full: EMIT
@@ -154,7 +154,7 @@ set HDR-NFA here  ", CMOVE  #, 0  #, HDR-NFA  #, HDR-LINK  set HDR-LINK here
 \ list of refusals owed, and messages written and read a word at a time
 \ (MESH.md 7a, 7b, 7c.6).  The ports themselves are still written a word at
 \ a time for the two things that are not messages: a newborn node's
-\ nucleus (PORT!, quit.v4) and a node's requests to its kernel.
+\ nucleus (PORT!, quit.f18) and a node's requests to its kernel.
 \
 \ THE STACKS.  All of this runs on the stacks the node's text is using.
 \ (SERVE) and what it calls keep to four cells of the data stack and four
@@ -228,7 +228,7 @@ set HDR-NFA here  ", CMOVE  #, 0  #, HDR-NFA  #, HDR-LINK  set HDR-LINK here
 \ words are in (IN), is refused.  A refusal for this node itself -- its own
 \ message came back to it -- is counted in (REFUSED) as one that came by a
 \ wire would be; or, if it is about the node this one is waiting on,
-\ (A-SELF) is set for AWAIT to find (quit.v4).
+\ (A-SELF) is set for AWAIT to find (quit.f18).
 \ (WIRE) is not what it was afterwards: the NACK went by another.
 \ If the drop does not drop -- the wire was cut after the message was looked
 \ at, which let it go already -- nothing is counted and no one is told.
@@ -392,7 +392,7 @@ set HDR-NFA here  ", CMOVE  #, 0  #, HDR-NFA  #, HDR-LINK  set HDR-LINK here
 
 \ ( -- )   send what has been printed, to where (PRINT-TO) says, by the port
 \ (PRINT-PORT): a message of type 2, its characters four to a word, the
-\ first lowest.  quit.v4 sets those two when text for this node arrives.
+\ first lowest.  quit.f18 sets those two when text for this node arrives.
 \ It waits for room on the wire, and for the 8 cells kept as well when the
 \ wire is the one the answer goes by.  The characters are made ready in
 \ (OUT-TEXT), not where they are: until the message is on the wire the