Zero C-compiler warnings on all three architectures; fix real restore_vm_state() bug

Maintainability sweep (prompted by "this is getting hard to maintain"):
fixed the remaining three warning classes after the missing-field-
initializers commit -- 2x -Wsign-compare (control_words.c, cast at the
comparison site rather than changing cf_last_mode's type, which
deliberately holds a -999 sentinel outside vm_mode_t's valid range),
2x -Wstringop-truncation (mkcapsule.c, strncpy+manual-null-terminate
replaced with the idiomatic snprintf equivalent), and 26x
-Wunused-parameter (mostly documented stubs, silenced with the repo's
existing (void)param; idiom).

One of the unused-parameter warnings was not a deliberate stub -- a
real bug. restore_vm_state() (test_common.c) is named, documented, and
called by nine real call sites (acl_words_test.c x8 plus its own
internal use) as "restore saved VM state", but ignored all four of its
parameters and hard-reset to a fixed baseline instead, silently not
restoring what any caller actually saved. Fixed to actually assign the
passed-in dsp/rsp/error/mode. Found while fixing warnings, reported
before touching it, fixed/tested/documented/committed on explicit
instruction.

Verified: all three architectures build with zero C-compiler warnings
(amd64: 3040 -> 0; aarch64's one remaining note is lld-link's own
unrelated linker warning, not a C warning). Full amd64 acceptance boot
post-fix: POST 1003/965/0/0/38 (total/passed/failed/errors/stubs),
"ALL IMPLEMENTED TESTS PASSED!", contract checks (A4'/A1) all passed,
dict_hash=0x24b4279f0670aa3a -- an exact match to this document's own
previously-recorded baseline hash.

.claude/CLAUDE.md corrected to describe the real -Wno-error= exemption
list instead of the "-Wall -Werror" oversimplification. FABRIC-2.md
Section J records the full sweep, including doc-tree staleness findings
flagged but not fixed this pass (docs/lithosananke/ROADMAP.md branch
topology, docs/03-architecture/word-acl/DESIGN.md's Phase 7 claim
contradicting CLAUDE.md, top-level ROADMAP.md's stale StarForth-era
status, the Isabelle pipeline-metrics model mismatch).

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

src/word_source/control_words.c

@@ -124,7 +124,7 @@ static inline void cf_epoch_sync(VM *vm) {
         cf_last_mode = vm->mode;
         return;
     }
-    if (vm->mode != cf_last_mode) {
+    if ((int)vm->mode != cf_last_mode) {
         cf_sp = -1;
         cf_last_mode = vm->mode;
         log_message(LOG_DEBUG, "CF: reset (mode transition)");

src/word_source/io_words.c

@@ -71,6 +71,7 @@ static void io_word_emit(VM *vm) {
  *          Outputs a newline character to the terminal
  */
 static void io_word_cr(VM *vm) {
+    (void)vm;
     putchar('\n');
     fflush(stdout);
 }
@@ -146,6 +147,7 @@ static void io_word_type(VM *vm) {
  *          Outputs a single space character to terminal
  */
 static void io_word_space(VM *vm) {
+    (void)vm;
     putchar(' ');
     fflush(stdout);
 }

src/word_source/string_words.c

@@ -334,6 +334,7 @@ void string_word_bracket_tick(VM *vm) {
 
 /* LITERAL / [LITERAL] are placeholders here */
 void string_word_literal(VM *vm) {
+    (void)vm;
 }
 
 void string_word_bracket_literal(VM *vm) { string_word_literal(vm); }