test: migrate Fam13 misc checker/coercion value tests to @test (#5-C6)

Final fold-2 chunk. The 12 Fam13 single-file value drivers move from
test/wcc/*_run.c into in-language @test row-tables under test/lang/:

- value rows -> test/lang/*_test.ww (12 files)
- reject rows -> runww //ww:error carriers (13, dual-stage non-vacuous)
- nullable abort rows -> runww //ww:run-exit 1 carriers (3)
- 953_globalslice_arg -> _runonly (cs!=ww checker divergence, #28)
- 788 value_not_type_neg + 953_arrlit_slice reject_assign kept as slim
  rc-only .c pins (divergent-diag dual-reject, mutation-gated); 788 #29

Coverage parity verified row-by-row vs each retired driver; advisor-
ratified carve taxonomy; two-round reviewed. Floor ratchet follows.

test/lang/arrlit_elem_narrow_test.ww

@@ -0,0 +1,46 @@
+// arrlit_elem_narrow_test — #251: narrow int/rune array-literal elements to a
+// declared [N]T element type at the let / def / struct-field init sites.
+// Migrated from test/wcc/951_arrlit_elem_narrow_run.c (accept rows; cs==ww
+// byte-id rides T2). The out-of-range and str-elem reject rows stay as runww
+// //ww:error carriers under test/wcc/data/.
+//
+// Pre-#251 cstage REJECTED in-range bare-int/rune lits at local let/def/struct
+// ("[4]i32 not assignable to [4]u8"); wwstage SILENTLY over-accepted out-of-
+// range/str at def + struct-field (a rule-7 miscompile). Element WIDTH is
+// declared-type-driven at cgen, so the byte-id gate confirms the emitted bytes
+// are u8-wide regardless of the literal node type.
+
+package arrlit_elem_narrow_test;
+
+type enc = struct { m: [4]u8 };
+
+def D_int: [4]u8 = [65, 66, 67, 68];
+def D_rune: [4]u8 = ['A', 'B', 'C', 'D'];
+let E: enc = enc { m = [65, 66, 67, 68] };
+
+@test fn let_int() void = {
+	let a: [4]u8 = [65, 66, 67, 68];
+	assert(a[0]: i32 == 65);
+};
+
+@test fn let_rune() void = {
+	let a: [4]u8 = ['A', 'B', 'C', 'D'];
+	assert(a[0]: i32 == 65);
+};
+
+@test fn def_int() void = {
+	assert(D_int[0]: i32 == 65);
+};
+
+@test fn def_rune() void = {
+	assert(D_rune[0]: i32 == 65);
+};
+
+@test fn struct_int() void = {
+	assert(E.m[0]: i32 == 65);
+};
+
+@test fn struct_rune() void = {
+	let e: enc = enc { m = ['A', 'B', 'C', 'D'] };
+	assert(e.m[1]: i32 == 66);
+};