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/compile.f18

@@ -1,15 +1,15 @@
-\ compile.v4 -- the interpreter's inner loop, and the defining and compiling
+\ compile.f18 -- the interpreter's inner loop, and the defining and compiling
 \ words.
 \
 \ DECOMPOSITION.md 5.17 and 5.18: STATE [ ] : ; EXIT IMMEDIATE LITERAL COMPILE
 \ [COMPILE] ' EXECUTE CREATE VARIABLE CONSTANT DOES>, the control structures
 \ IF ELSE THEN BEGIN UNTIL AGAIN WHILE REPEAT DO ?DO LOOP +LOOP, and INTERPRET,
 \ which they cannot be run without.  Part of the compiler capsule.  Rests on
-\ core.v4, input.v4, dict.v4 and codegen.v4.
+\ core.f18, input.f18, dict.f18 and codegen.f18.
 \
 \ HOW A WORD IS COMPILED.  v4 code is native: a colon definition is
 \ instruction words, and compiling a word into one lays down a call to it.
-\ Two flags on an entry (dict.v4) change that:
+\ Two flags on an entry (dict.f18) change that:
 \   inline        its code is a straight run of opcodes and literals ending
 \                 in ; -- that run is copied in place of a call.  Everything
 \                 that touches the return stack must be, since a call would
@@ -46,9 +46,9 @@ macro ROT   push SWAP pop SWAP   endmacro
 \ ( -- )   give up the line: stop compiling, forget the word being built and
 \ whatever control structures were open, skip the rest of the input, and set
 \ NODE-ERROR.  A definition that was under way stays hidden.  It returns to
-\ whatever called INTERPRET, which is QUIT (quit.v4): QUIT sees NODE-ERROR
+\ whatever called INTERPRET, which is QUIT (quit.f18): QUIT sees NODE-ERROR
 \ and prints ERROR.
-\ (ABANDON-AS) is the same with an error code (core.v4) for the prompt to
+\ (ABANDON-AS) is the same with an error code (core.f18) for the prompt to
 \ print the message of.
 : (ABANDON-AS) ( code -- )
   (C)+9 a! !
@@ -150,7 +150,7 @@ set HDR-NFA here  ", EXECUTE  #, 0  #, HDR-NFA  #, HDR-LINK  set HDR-LINK here
 
 \ ( -- n flag )   the word WORD has just left, as a single-cell number in the
 \ current BASE, and -1; or 0 0 if it is not one.  A leading minus sign is
-\ allowed.  This is what the interpreter uses: NUMBER (input.v4) makes a
+\ allowed.  This is what the interpreter uses: NUMBER (input.f18) makes a
 \ double and needs more of the stack than can be spared here.
 \ (P)+2 the number so far, (P)+3 where it is in the word, (P)+4 the word's
 \ length, (P)+5 the sign, (P)+6 the base.