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— the issue is superseded and its behavior is covered by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/lsp/corpus_sweep.test.zig

@@ -8,7 +8,7 @@ const doc_mod = @import("document.zig");
 // issue corpora, in process. The contract is simply: analysis must complete
 // without a panic/abort for any file. A panic aborts the whole test binary —
 // that is the loud CI signal that some new AST node shape crashes the analyzer
-// (the bug class issue 0099 fixed at `sema.zig`'s `resolveTypeNode`). Files
+// (the bug class fixed at `sema.zig`'s `resolveTypeNode`). Files
 // that merely fail to parse or sema cleanly are fine: `analyzeDocument` records
 // a null index and returns, which counts as a clean (non-crashing) outcome.
 //