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— the issue is superseded and its behavior is covered by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/types.zig

@@ -45,7 +45,7 @@ pub const Type = union(enum) {
     /// `is_raw` records whether the inner type-name came from a backtick raw
     /// reference (`` `s2 ``) or an already-resolved user type. It is the
     /// `skip_builtin` the resolver MUST pass when re-resolving the stored inner
-    /// name (issue 0089) — without it `resolveTypeNameStr` would reclassify a
+    /// name — without it `resolveTypeNameStr` would reclassify a
     /// user type named `s2` as the builtin int, diverging from codegen. The
     /// field is REQUIRED (no default) so a future construction site cannot
     /// silently drop the bit, the way the LSP index did for compound shapes.
@@ -79,7 +79,7 @@ pub const Type = union(enum) {
         /// null = the dimension could not be folded to a compile-time integer
         /// by the editor index (an identifier const it couldn't resolve, or a
         /// non-const expression). Explicit "unknown" rather than a fabricated
-        /// concrete length — this is hover/metadata, not codegen (issue 0099).
+        /// concrete length — this is hover/metadata, not codegen.
         length: ?u32,
         is_raw: bool,
     };
@@ -216,7 +216,7 @@ pub const Type = union(enum) {
         if (node.data != .type_expr) return null;
         // A backtick raw type reference (`` `s2 ``) is the LITERAL name used as
         // a type — it must skip this builtin/reserved classifier and resolve
-        // through user-defined types only (issue 0089), mirroring the codegen-
+        // through user-defined types only, mirroring the codegen-
         // side `resolveNamed`'s `skip_builtin`. Returning null lets the sema
         // callers fall through to their struct/enum/alias registry lookup.
         if (node.data.type_expr.is_raw) return null;