feat(v4.0.0): the host node's stacks are 32 deep (D-17)

With the stacks counted and guarded (D-16) their size is a parameter of
the node.  The host node, which runs the interpreter and the compiler
under the user's programme, gets 32 values and 32 return entries; a mesh
node keeps the F18's 10 and 9.  Nothing else about the mechanism or any
word's definition changes.

- stack.h: V4_DATA_RING and V4_RET_RING are build parameters; the
  Makefile sets them for the host-node tests.
- tests/test_host_quit.c no longer assumes a size: it fills the stacks to
  whatever they are, and takes every exit with the return stack full.
- Measured on the host node now: 28 values on a line, 29 waiting between
  lines, words 31 deep from the prompt.

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

v4/capsule/forth.v4

@@ -23,8 +23,8 @@ header 2DROP inline     : 2DROP   drop drop ;
 \ DEPTH reads the stack register.  PICK and ROLL reach under the top of a
 \ stack that has no addresses: the values above the one wanted are set aside
 \ in (S), and put back.  (F)+3 how many are still to set aside, (F)+4 where
-\ the next goes, (F)+5 the value wanted, (F)+6 how many are set aside.  With nine values and n on the
-\ stack it is full, so until a value has been set aside nothing here pushes
+\ the next goes, (F)+5 the value wanted, (F)+6 how many are set aside.  With n on top of a stack that is
+\ otherwise one short of full there is no room at all, so until a value has been set aside nothing here pushes
 \ anything while n is still there, and never more than one cell after.
 
 \ FORTH-79: how many values were on the stack before DEPTH