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/compile.v4

@@ -17,8 +17,9 @@
 \   compile-only  it may not be executed by the interpreter.
 \ An immediate word is executed even when compiling.
 \
-\ THE STACKS ARE SHORT (D-2): ten cells of data, nine return entries, and one
-\ more of either is a fault (D-16).  The interpreter and compiler run on the same
+\ THE STACKS ARE SHORT: written for ten cells of data and nine return entries
+\ (D-2; the host node now has 32 of each, D-17), and one more of either is a
+\ fault (D-16).  The interpreter and compiler run on the same
 \ stacks as the user's words, with the user's values beneath them, so:
 \   - every word here keeps what it works on in (C), and has at most three
 \     cells of its own on the data stack at any moment;