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".

test/wcc/610_arch.c

@@ -13,6 +13,7 @@
 #include <unistd.h>
 #include <sys/stat.h>
 #include <sys/wait.h>
+#include "wwtestpkg.h"
 
 static int run(const char *cmd) { return system(cmd); }
 
@@ -33,24 +34,26 @@ main(void)
 	snprintf(dir, sizeof dir, "/tmp/wwarch_%d", getpid());
 	mkdir(dir, 0755);
 
-	/* lib_good.ww — defines f1() */
+	/* lib_good.ww — defines f1() (→ main.f1 under strict-package #24a) */
 	char path[256];
 	snprintf(path, sizeof path, "%s/lib_good.ww", dir);
 	FILE *f = fopen(path, "wb");
-	fputs("export fn f1() i32 = { return 7; };", f);
+	wwtest_fputs("export fn f1() i32 = { return 7; };", f);
 	fclose(f);
 
 	/* lib_bad.ww — defines f2() but also references an undefined extern */
 	snprintf(path, sizeof path, "%s/lib_bad.ww", dir);
 	f = fopen(path, "wb");
-	fputs("@symbol(\"this_symbol_does_not_exist\") fn bogus() i32;\n"
+	wwtest_fputs("@symbol(\"this_symbol_does_not_exist\") fn bogus() i32;\n"
 	      "export fn f2() i32 = { return bogus(); };", f);
 	fclose(f);
 
-	/* main.ww — calls f1, NOT f2 */
+	/* main.ww — calls f1, NOT f2. The plain prototype declares f1 in the
+	 * same (main) module, so the call resolves to main.f1 — matching
+	 * lib_good's moduled definition (no @symbol bare-pin needed). */
 	snprintf(path, sizeof path, "%s/m.ww", dir);
 	f = fopen(path, "wb");
-	fputs("@symbol(\"f1\") fn f1() i32;\n"
+	wwtest_fputs("fn f1() i32;\n"
 	      "fn main() i32 = { return f1(); };", f);
 	fclose(f);