issues: relocate legacy examples/issue-* repros into issues/

Clear the examples/issue-* namespace (new layout keeps open-issue repros under
issues/, co-located with their .md). Two legacy files:

- issue-0030 was a feature-request placeholder (trivial main, no real test).
  `extern G : T;` cross-file sx globals are still unimplemented (parse error),
  so it's an open feature request: issues/0030-extern-global-declarations.{md,sx}.
- issue-0019 was a broken/superseded multi-file fixture (relative imports, not
  runnable from root; the non-transitive-#import scenario is covered by the
  passing 0706-modules-import-non-transitive). Moved to
  issues/0019-import-non-transitive-c-scope/ with a status note; safe to delete.

Suite unchanged: 324 passed.

issues/0019-import-non-transitive-c-scope/c_wrapper.sx

@@ -0,0 +1,10 @@
+// This module imports C functions and provides wrappers
+#import c {
+    #include "vendors/test_c/test.h";
+    #source "vendors/test_c/test.c";
+};
+
+// Wrapper function that calls the C function
+wrapped_add :: (a: s32, b: s32) -> s32 {
+    add_numbers(a, b);
+}

issues/0019-import-non-transitive-c-scope/main_bad.sx

@@ -0,0 +1,18 @@
+// Test: other.sx calls C functions without importing the C module
+// main imports both c_wrapper.sx and other.sx
+// other.sx should NOT have access to C functions from c_wrapper
+#import "../modules/std.sx";
+#import "c_wrapper.sx";
+#import "other.sx";
+
+main :: () -> s32 {
+    // This works: we import c_wrapper so we have transitive access
+    result := wrapped_add(10, 20);
+    print("wrapped_add(10, 20) = {}\n", result);
+
+    // This calls other.sx's function which tries to call add_numbers
+    // other.sx did NOT import c_wrapper.sx, so this should fail
+    bad := use_c_directly();
+    print("use_c_directly() = {}\n", bad);
+    0;
+}

issues/0019-import-non-transitive-c-scope/main_good.sx

@@ -0,0 +1,10 @@
+// Test: calling wrapper functions works (we import the module)
+#import "../modules/std.sx";
+#import "c_wrapper.sx";
+
+main :: () -> s32 {
+    // This should work: calling the sx wrapper
+    result := wrapped_add(10, 20);
+    print("wrapped_add(10, 20) = {}\n", result);
+    0;
+}

issues/0019-import-non-transitive-c-scope/other.sx

@@ -0,0 +1,6 @@
+// This file does NOT import c_wrapper.sx
+// It should NOT be able to call add_numbers
+
+use_c_directly :: () -> s32 {
+    add_numbers(5, 3);
+}