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— the issue is superseded and its behavior is covered by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

@@ -637,7 +637,7 @@ pub const Parser = struct {
             // bare name (so `` `s2(s64) ``, `` `s2.Inner ``, `` *`s2 `` all
             // parse); it is threaded onto the final `type_expr` /
             // `parameterized_type_expr` so resolution skips the builtin
-            // classifier and looks up a `` `s2 ``-declared type (issue 0089).
+            // classifier and looks up a `` `s2 ``-declared type.
             const atom_is_raw = self.current.is_raw;
             var name = self.tokenSlice(self.current);
             self.advance();
@@ -2738,7 +2738,7 @@ pub const Parser = struct {
                 const is_raw = self.current.is_raw;
                 // A backtick raw identifier (`` `s2 ``) is NEVER type-classified —
                 // it is always a value identifier, bypassing the reserved-type-name
-                // rule (issue 0089). Only a bare spelling is checked for a type name
+                // rule. Only a bare spelling is checked for a type name
                 // (e.g. s32, u8, s128).
                 if (!is_raw and Type.fromName(name) != null) {
                     self.advance();