Fix systemic -Wmissing-field-initializers across src/test_runner/modules/ (3010 -> 0)

TestCase gained a trailing `contract` field (WordContract) at some point
after all 20 test-module files' compound literals were written -- every
single TestCase/WordTestSuite initializer in the tree (sentinels, real
entries, and per-suite entries) omitted it, producing ~3010 warnings on
every build. CLAUDE.md's own documentation claimed this was isolated to
one file (vocabulary_words_test.c); a full audit found it systemic
across all 20 files.

Fixed mechanically: added the missing `{0}` trailing initializer
everywhere. Semantically a no-op -- C99 already zero-fills unlisted
trailing struct fields, so this only silences the diagnostic, changes
no behavior. Verified: all three architectures (amd64/aarch64/riscv64)
build clean, remaining warning count unchanged (30, matching the other
three known -Wno-error-exempted classes: unused-parameter, sign-compare,
plus mkcapsule.c's stringop-truncation which was never actually gated
by this policy -- it's a separate host tool with no -Werror at all).

.claude/CLAUDE.md corrected to describe the actual -Wno-error= exemption
list (four classes, not "build with -Wall -Werror" unconditionally) and
the real current warning inventory.

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

.claude/CLAUDE.md

@@ -446,9 +446,23 @@ status for kernel work.
 ## Code Standards
 
 - **Strict ANSI C99** — No GNU extensions, no C++ features
-- **Zero warnings target** — Build with `-Wall -Werror`; note `-Wmissing-field-initializers`
-  warnings have been observed in `src/test_runner/modules/vocabulary_words_test.c` during a
-  full kernel build — worth reporting if it recurs, not silently patched
+- **Zero warnings target, with four explicit exceptions — corrected 2026-08-18, previous
+  claim was wrong.** Build with `-Wall -Wextra -Werror`, but `Makefile.starkernel` carries
+  `-Wno-error=unused-parameter -Wno-error=shift-negative-value -Wno-error=sign-compare
+  -Wno-error=missing-field-initializers` — those four classes are enabled (still visible as
+  warnings) but deliberately downgraded from fatal, everything else is. The previous version
+  of this line claimed `-Wmissing-field-initializers` was isolated to one file
+  (`vocabulary_words_test.c`) — that was never accurate; a full audit found it systemic
+  across 20 files in `src/test_runner/modules/` (all missing the same later-added
+  `TestCase.contract`/`WordTestSuite.suite_contract` trailing field, ~3,010 instances). Fixed
+  in place across all 20 files (mechanical: added the missing `{0}` initializer, semantically
+  a no-op since C99 already zero-fills unlisted trailing fields — the fix only silences the
+  diagnostic). Verified clean on all three architectures. Remaining, still-open warnings as
+  of the same audit: 26 `-Wunused-parameter` (scattered, several files, not yet fixed), 2
+  `-Wsign-compare` (`control_words_test.c:127`), and 2 `-Wstringop-truncation` in
+  `tools/mkcapsule.c` — that last one is a separate host build tool compiled via plain `cc
+  -Wall -Wextra -O2` (no `-Werror` at all), never actually gated by this policy in the first
+  place, genuinely unfixed rather than exempted.
 - **No hidden state** — All VM state is explicit in the `VM` struct
 - **Platform-agnostic** — Kernel code gated by `__STARKERNEL__` and `STARFORTH_ENABLE_VM`
 - **Content-addressed immutability** — Capsule ID = content hash; any mutation is detectable