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— the issue is superseded and its behavior is covered by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

@@ -75,7 +75,7 @@ pub const CallPlan = struct {
         /// The single bare-call author `selectPlainCallableAuthor` selected for a
         /// genuine flat same-name collision (R5 §#3). Carries the resolved
         /// `*FnDecl` + source so `plan` and the lowering call-path read ONE
-        /// author and can no longer disagree (fix-0102 F2); the FuncId is
+        /// author and can no longer disagree; the FuncId is
         /// materialized on demand. Only set when the bare name reroutes away from
         /// the first-wins winner; the common path still uses `func` / `named`.
         selected: Lowering.SelectedFunc,
@@ -159,7 +159,7 @@ pub const CallResolver = struct {
             // Plain bare same-name flat collision (R5 §C): route through the ONE
             // author producer `selectedFreeAuthor` so `plan` types the call as the
             // SAME author the lowering call-path binds — they can no longer
-            // disagree (fix-0102 F2). A generic / foreign / builtin author is not
+            // disagree. A generic / foreign / builtin author is not
             // plain-free so the producer returns `.none`; `.ambiguous` / `.none`
             // fall through to the first-wins path below, byte-for-byte.
             switch (self.selectedFreeAuthor(c)) {
@@ -319,7 +319,7 @@ pub const CallResolver = struct {
                 // routes through the SAME author producer `selectedFreeAuthor` as a
                 // bare call, so the planned target / return type IS the author
                 // lowering dispatches — they can't disagree under a flat same-name
-                // collision (fix-0102 F2 / R5 §C). Without this, plan typed the
+                // collision (R5 §C). Without this, plan typed the
                 // first-wins winner while lowering bound the selected shadow,
                 // mis-tagging the call's result (a string-typed winner over an s64
                 // shadow boxes a raw int as a string pointer → segfault).
@@ -451,7 +451,7 @@ pub const CallResolver = struct {
     /// verdict (R5 §#3). Both `plan` (typing, via its `.selected` arm) and
     /// `lowerCall` (default expansion / param typing / dispatch) consume THIS one
     /// result, so they can never pick different same-name authors for the same
-    /// call (fix-0102 F2). Side-effect-free: it consults ONLY the author selector
+    /// call. Side-effect-free: it consults ONLY the author selector
     /// (`selectPlainCallableAuthor`) — never return-type inference or type-arg
     /// resolution — so `lowerCall` can compute it eagerly without emitting a
     /// premature diagnostic the full `plan` would (e.g. `cast(type)`'s type-arg).