Move vocabulary and control-flow state off file-scope statics onto VM

proof/FINDINGS.md's Isabelle/HOL word-source sweep (§1) found the two
defects severe enough to actively corrupt the live Tripod multi-VM fleet:
file-scope C statics standing in for state that belongs on struct VM.

- vocabulary_words.c (highest severity in the sweep): forth_vocab/
  context_vocab/current_vocab, context_var_addr/current_var_addr, the
  ctx_fc/forth_fc first-char search index, and the `initialized` guard
  were all process-wide statics. Only the first VM to touch any
  vocabulary word ever ran setup; every VM after that silently shared
  VM #1's dictionary-chain pointers and reused VM #1's byte-offset
  addresses as if valid in its own vm->memory. One VM's VOCABULARY/
  DEFINITIONS/FORTH silently changed where every other VM looked up and
  defined words.

- control_words.c: cf_stack/cf_sp/cf_last_mode (IF/THEN/BEGIN/DO/CASE
  compile-time nesting) and the LEAVE/ENDOF patch-site bookkeeping
  (leave_addrs/leave_sp/leave_mark_*, endof_addrs/endof_sp/endof_mark_*)
  were also process-wide statics. Two VMs compiling colon definitions at
  overlapping times would corrupt each other's nesting state.

Both moved onto struct VM, following the existing hold_addr/hold_pos
precedent in include/vm.h ("lives in each VM's own memory... so child
VMs never alias Hera's buffer"):

- New VocabularyState struct (vm->vocab): chain heads, VM-cell addresses,
  first-char index, initialized flag.
- New ControlFlowState struct (vm->cf): cf_stack/cf_sp/cf_last_mode plus
  the LEAVE/ENDOF patch-site stacks. cf_tag_t/cf_item_t/CF_STACK_MAX
  moved from control_words.c into include/vm.h since they're now part of
  the struct VM field's type.
- Sentinel fields (-1/-999, meaning "empty") explicitly initialized in
  both vm_init_with_host() implementations (hosted src/vm_bootstrap.c and
  kernel src/starkernel/vm/vm_bootstrap.c) alongside the existing
  dsp/rsp = -1 initialization, since the preceding zero-init leaves them
  at 0 rather than their empty sentinel.

Every word function in both files already took VM *vm, so no call sites
outside these two files needed to change; cf_push_item/cf_pop_item/
cf_peek_item gained a VM* parameter to reach vm->cf.

Verified: hosted (amd64) and kernel (amd64, __STARKERNEL__) both build
clean with -Wall -Werror after a full clean rebuild (struct VM's layout
changed size, and this Makefile has no header-dependency tracking, so a
stale incremental build would have linked mismatched object layouts).
Hosted POST suite 1012/1012 passing (0 regressions). Manually exercised
VOCABULARY/DEFINITIONS/FORTH/ORDER, and IF/ELSE, DO/LOOP/LEAVE,
BEGIN/WHILE/REPEAT, and CASE/OF/ENDOF/ENDCASE (including nested DO with
I/J) in the REPL -- all correct and unchanged from pre-refactor behavior.

Note: a pre-existing CASE/ENDCASE default-clause bug (the code after the
last OF...ENDOF pair does not correctly become the "default" value once
DROP runs) was found while testing this refactor and confirmed present
on unmodified master too -- not touched here, out of scope for this pass.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_014Qf6YcnHgaEtEygq3knx19

proof/FINDINGS.md

@@ -47,6 +47,15 @@ the two that would actually corrupt VM behavior in the live Tripod fleet
 today, if two VMs exercise them concurrently. Worth scoping as a real fix
 independent of this proof work — moving these into `struct VM` fields.
 
+**RESOLVED 2026-09-05:** both #1 and #5 moved onto `struct VM`, following
+the `hold_addr`/`hold_pos` precedent already in `include/vm.h`. `vocabulary_words.c`'s
+chain heads, VM-cell addresses, first-char index, and `initialized` guard
+now live at `vm->vocab` (a new `VocabularyState` struct); `control_words.c`'s
+`cf_stack`/`leave_*`/`endof_*` bookkeeping now lives at `vm->cf` (a new
+`ControlFlowState` struct). Every word function in both files already took
+`VM *vm`, so no call sites outside these two files needed to change. #2, #3,
+#4, #6, #7 remain open — out of scope for this pass.
+
 ---
 
 ## 2. Missing overflow/capacity guards before stack pushes