parse: enforce strict-package — reject package-less files (#24a)

Flip the soft-default to a hard "missing package clause" error symmetrically in
both stages (cmd/wcc/parse.c + lib/ww/syntax/parse.ww): the first real decl of a
primary section with empty pathmod/resetmod and no seen clause is now rejected.
Closes the documented soft-default divergence (the 63-wrapper carve-out).

The gate flip can't be split from the migration it breaks, so this is one atomic
commit: ~80 test/wcc wrappers gain `package main;` via a shared wwtestpkg.h
helper, 6 data fixtures plus 17 asm-grep assertions update for the bare->main.<leaf>
root-helper mangle shift, and rt/ declares `package rt;` with @symbol pinning the
bare rt_ensure/rt_malloc linker names.

Root mangling narrows: the executable entry `main` stays bare (existing
carve-out), but root helper symbols become main.X. The #84 cluster is rewritten
to assert main.run distinct from aa.run/test.run; its cgen fix and bare machinery
are retained — still load-bearing for package-less module-reset deps. New
table-driven test 782_strict_package.c (6 rows, both stages).

Retiring //ww:module-reset is deferred to #24b: it is load-bearing (clears the
.wwi pathmod so the body's package clause asserts), not a vestige; fusing its
removal here would be a silent mismatch.

All byte-id gates green; full make test reports "all 335 tests passed".

Makefile

@@ -411,6 +411,7 @@ TESTS	= $(BIN)/test_smoke $(BIN)/test_lex $(BIN)/test_parse $(BIN)/test_check \
 	  $(BIN)/test_star_fn_deref \
 	  $(BIN)/test_star_fn_deref_call \
 	  $(BIN)/test_match_variant_dispatch \
+	  $(BIN)/test_strict_package \
 	  $(BIN)/test_io_types_run \
 	  $(BIN)/test_dot_aliased_ptr \
 	  $(BIN)/test_return_tagged_forward \
@@ -649,6 +650,13 @@ $(BIN)/test_unknowndecl_reject: test/wcc/989_unknowndecl_reject.c \
 		$(LIB)/libwwrt.a | $(BIN)
 	$(CC) $(CFLAGS) -o $@ $<
 
+# 782_strict_package (#24a): every primary section must open with a `package`
+# clause; a missing clause on the first decl is a hard error, symmetric on
+# cstage w6c + wwstage w6c_ww. Each reject row reddens under a gate revert.
+$(BIN)/test_strict_package: test/wcc/782_strict_package.c \
+		$(BIN)/w6c $(BIN)/w6c_ww | $(BIN)
+	$(CC) $(CFLAGS) -o $@ $<
+
 # 989_nullableglobal_reject (#45 silent->loud bridge, task #15 prereq): a
 # module-level nullable `(*T | void)` GLOBAL has no storage path, so a
 # match/is/as on it silently miscompiled (0(BP) read / undefined ref) on