wcc: array-init accept-if-fits coercion (#130, merges #146)

Align bare-int array-init assignability to Hare's literal-fits rule
(ref/harec/src/types.c promote_flexible): accept untyped-int array
elements that FIT the element type, reject out-of-range loud. cstage
(rejected all bare-int arrays, over-strict) and wwstage (accepted +
silently truncated out-of-range, over-loose) converge to the same
accept-if-fits rule. Per-element: foldable int literal range-checked
against element type [min,max] via def_cast_fits (rule-13 type-table
widths); non-foldable element falls back to type_assignable.

cstage: new arrlit_init_fits, N_LET decl-check fallback after whole-
array type_assignable fails. wwstage: checkletassign array branch +
route top-level lets through checkletassign (were unchecked — only
function-body lets ran assignability; closes #146 wwstage str->u8
over-accept).

Scalar-init range-check (let X:u8=300 truncates, both stages,
pre-existing) deferred to #148 — language-wide, needs bootstrap audit
+ explicit-cast conversion. def-array accept-if-fits deferred to #151
(def constfold machinery, different risk). Both bootstrap-NEUTRAL.

Test 920 (14 rows — accept: in-range u8/u32/u64/i32 + u8/i8 boundary +
typed regression + non-foldable-body; reject: over-range + over-256 +
i8-over + neg-for-unsigned + str->u8 + non-foldable-wider). Non-
foldable else-branch cs==ww verified (matching-type accept + byte-id;
wider-runtime-int reject both stages). Make test: 183/183 incl 990-997
byte-id + combined_ww_fresh.

Makefile

@@ -342,6 +342,7 @@ TESTS	= $(BIN)/test_smoke $(BIN)/test_lex $(BIN)/test_parse $(BIN)/test_check \
 	  $(BIN)/test_def_float_lit_run \
 	  $(BIN)/test_struct_composite_init_run \
 	  $(BIN)/test_array_static_init_run \
+	  $(BIN)/test_array_init_acceptiffits_run \
 	  $(BIN)/test_f64cgen_run \
 	  $(BIN)/test_f64crossmod_run \
 	  $(BIN)/test_tuprecv_run \
@@ -1165,6 +1166,11 @@ $(BIN)/test_array_static_init_run: test/wcc/919_array_static_init_run.c \
 		$(LIB)/libwwrt.a | $(BIN)
 	$(CC) $(CFLAGS) -o $@ $<
 
+$(BIN)/test_array_init_acceptiffits_run: test/wcc/920_array_init_acceptiffits_run.c \
+		$(BIN)/ww $(BIN)/w6c $(BIN)/w6c_ww $(BIN)/w6a $(BIN)/w6l \
+		$(LIB)/libwwrt.a | $(BIN)
+	$(CC) $(CFLAGS) -o $@ $<
+
 $(BIN)/test_f64cgen_run: test/wcc/951_f64cgen_run.c $(BIN)/ww $(BIN)/w6c \
 		$(BIN)/w6a $(BIN)/w6l $(LIB)/libwwrt.a | $(BIN)
 	$(CC) $(CFLAGS) -o $@ $<