feat(v4.0.0): block storage, LOAD and LIST (D-19)

- The golden model's host node gets a block storage device: four
  memory-mapped registers (number, address, command, status), 1024-byte
  blocks as 256 cells.  tests/test_node.c.
- capsule/blocks.v4: BLOCK BUFFER UPDATE SAVE-BUFFERS EMPTY-BUFFERS LIST
  LOAD SCR BLK (FORTH-79) and v3's FLUSH THRU and -->, over two buffers.
- The text being interpreted is at the address in (SRC), which QUERY makes
  the terminal's buffer and LOAD a block's; LOAD saves and restores it, so
  blocks nest and the rest of LOAD's line runs afterwards.  WORD makes
  sure a loading block is still in a buffer before it reads.
- In a block, \ skips to the next 64-character line.
- A block number that does not exist, and --> at the terminal, are errors
  with messages (D-18).
- tests/test_host_quit.c: ten transcripts of the v3 binary; nesting three
  deep on two buffers; what reaches the device and when.

v3's LOAD drops the rest of its line, and v3 has no BLK.

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

v4/capsule/quit.v4

@@ -22,7 +22,8 @@
 \ the data stack too.  A store to RSTACK-DEPTH or DSTACK-DEPTH does that.
 \
 \ Constants the loader supplies:
-\   (Q)     word address of two cells of scratch for this file
+\   (Q)     word address of four cells of scratch, which system.v4 and
+\           blocks.v4 use too
 \   DSTACK-DEPTH RSTACK-DEPTH   word addresses of the stack registers
 
 \ ( -- )   empty the return stack.  `a` is only something to store: any
@@ -46,6 +47,7 @@ macro R-CLEAR   RSTACK-DEPTH b! a !b   endmacro
   GO: drop
   READ:
   $203E6B6F (EMIT4)                                                   \ "ok> "
+  0 BLK a! !                                                          \ the terminal, whatever was being loaded
   QUERY
   0 NODE-ERROR b! !b
   INTERPRET
@@ -96,7 +98,7 @@ header ABORT
   -if POS  drop  2 jump (REPL)
   POS: -1 + if M1  -1 + if M2  -1 + if M3  -1 + if M4
        -1 + if M5  -1 + if M6  -1 + if M7  -1 + if M8  -1 + if M9
-       -1 + if M10  -1 + if M11  -1 + if M12
+       -1 + if M10  -1 + if M11  -1 + if M12  -1 + if M13  -1 + if M14
        drop  2 jump (REPL)
   M1: drop  $6167654E (EMIT4) $65766974 (EMIT4) $756F6320 (EMIT4) $746E (EMIT4) CR  2 jump (REPL)
   M2: drop  $20746F4E (EMIT4) $756E2061 (EMIT4) $7265626D (EMIT4) CR  2 jump (REPL)
@@ -110,6 +112,8 @@ header ABORT
   M10: drop  $746F7250 (EMIT4) $65746365 (EMIT4) $6F772064 (EMIT4) $6472 (EMIT4) CR  2 jump (REPL)
   M11: drop  $69766944 (EMIT4) $6E6F6973 (EMIT4) $20796220 (EMIT4) $6F72657A (EMIT4) CR  2 jump (REPL)
   M12: drop  $75677241 (EMIT4) $746E656D (EMIT4) $74756F20 (EMIT4) $20666F20 (EMIT4) $676E6172 (EMIT4) $65 (EMIT4) CR  2 jump (REPL)
+  M13: drop  $636F6C42 (EMIT4) $756F206B (EMIT4) $666F2074 (EMIT4) $6E617220 (EMIT4) $6567 (EMIT4) CR  2 jump (REPL)
+  M14: drop  $62206F4E (EMIT4) $6B636F6C (EMIT4) $20736920 (EMIT4) $6E696562 (EMIT4) $6F6C2067 (EMIT4) $64656461 (EMIT4) CR  2 jump (REPL)
 
 \ The table the loader gives the node: six words, one for each kind of
 \ fault in the node's order, each a jump.  A jump fills its word, so they