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/dict.f18

@@ -1,9 +1,9 @@
-\ dict.v4 -- the dictionary: its space, its entries, and looking a name up.
+\ dict.f18 -- the dictionary: its space, its entries, and looking a name up.
 \
 \ DECOMPOSITION.md 5.12 and 5.13: HERE ALIGN ALLOT , C, 2, PAD LATEST, FIND ' ,
 \ and the entry-field words >LINK LFA LINK> >NAME NFA NAME> CFA PFA >BODY
 \ TRAVERSE SMUDGE HIDDEN.  Part of the compiler capsule: it runs on the host
-\ node.  Rests on core.v4 and input.v4.
+\ node.  Rests on core.f18 and input.f18.
 \
 \ AN ENTRY.  A word's execution address (xt) is the address of its code, and
 \ everything else is found from it:
@@ -129,7 +129,7 @@ set HDR-NFA here  ", HIDDEN  #, 0  #, HDR-NFA  #, HDR-LINK  set HDR-LINK here
 \ A word's code is here on the node; its accounts are a record its kernel
 \ keeps.  So the kernel has to be told of every entry that is made and of
 \ every entry that goes.  An entry is made in one place, (HEADER); entries go
-\ in two, FORGET and COLD (system.v4).  Each tells through a variable that
+\ in two, FORGET and COLD (system.f18).  Each tells through a variable that
 \ holds the xt of a word to run, or 0 for a node whose host keeps no records:
 \   (WORD-DEFINED)     ( xt -- )   an entry has been made; its code will be at xt
 \   (WORD-FORGOTTEN)   ( w -- )    every entry at word address w or above is gone
@@ -221,7 +221,7 @@ set HDR-NFA here  ", FIND  #, 0  #, HDR-NFA  #, HDR-LINK  set HDR-LINK here
 
 \ ( -- addr )   FORTH-79: the parameter field address of the next word in the
 \ input stream.  Not found is an error: 0, and NODE-ERROR is set.  This is '
-\ when interpreting; compile.v4 adds what ' does when compiling.
+\ when interpreting; compile.f18 adds what ' does when compiling.
 \ ( -- 0 )   say that the word WORD has just left is not known, as v3 does:
 \ UNKNOWN WORD: 'xxx'
 : (UNKNOWN)