cleanup: drop resolved-issue citations from src comments

Sweep all src/**.zig comments that cite resolved issues (issue NNNN /
fix-NNNN / KB-N): the invariant or mechanism each comment states is
kept; the historical citation is dropped, per the no-conclusion-comments
rule. Pure-history parentheticals are removed outright. References to
the 16 still-open issues (0030, 0041-0056) are untouched, as are test
NAMES carrying regression provenance (matching the sanctioned
"Regression (issue NNNN)" example-header convention).

Also removes the issues/0019-import-non-transitive-c-scope/ fixture dir
— the issue is superseded and its behavior is covered by
examples/0706-modules-import-non-transitive.sx (the .md writeup stays).
issues/0030's repro .sx stays: that issue is an open feature request.

Gate: zig build OK; zig build test 426/426; run_examples 541/0; zero
expected/ snapshot churn.

src/c_import.zig

@@ -129,7 +129,7 @@ pub fn processCImport(
                     .type_expr = ptype_node,
                     // Foreign C param names (`s1`, `s2`, …) are RAW — exempt from
                     // the reserved-type-name binding check; generated bindings
-                    // must import without hand-edits (issue 0089).
+                    // must import without hand-edits.
                     .is_raw = true,
                 });
             }
@@ -159,7 +159,7 @@ pub fn processCImport(
                     // A foreign C function whose own NAME collides with a reserved
                     // type spelling (`int s2(int);`) is RAW — exempt from the
                     // reserved-type-name decl check so generated bindings import
-                    // without hand-edits (issue 0089).
+                    // without hand-edits.
                     .is_raw = true,
                 } },
             };