fix(python): bare class references produce references edges to classes (#1478) (#1493)

Python's class-as-value idioms (return SomeClass, x = SomeClass, registry
dicts, classes passed as arguments) produced no references edges, so
callers/impact on a Django/DRF serializer missed the views that consume it.
Three gates dropped them:

- return_statement was never dispatched by PYTHON_SPEC (kernel mirrored)
- the extraction gate (definedHere) collected function/method names only
- resolution accepted function/method targets only (matchFunctionRef +
  the function_ref import fast path)

Capture return_statement for Python (single expression; tuple returns not
descended), admit same-file CLASS names to the gate, and accept class
targets for Python bare identifiers — scoped to Python so the TS/JS KIND
FILTER contract is untouched. The docopt false-positive mechanism behind
the function-only rule (lowercase locals vs same-named methods) doesn't
transfer: methods stay excluded for bare ids, and the same-file/import
gate + unique-or-drop rules still apply.

Probed on django-rest-framework (~250 files): 559 new references→class
edges, 10/10 sampled genuine (serializer_class = AuthTokenSerializer, the
ModelSerializer field-mapping registry, aliases, ctor args, isinstance).
EXTRACTION_VERSION 24 → 25.

Co-authored-by: Claude Fable 5 <noreply@anthropic.com>

codegraph-kernel/src/python.rs

@@ -250,7 +250,9 @@ impl<'t> Walker<'t> {
             target_id_str: NONE_STR,
         });
 
-        if kind == "function" || kind == "method" {
+        // Classes join the fn-ref gate for Python (#1478): class-as-value is
+        // a first-class idiom (mirrors flushFnRefCandidates' python branch).
+        if kind == "function" || kind == "method" || kind == "class" {
             self.defined_fn_names.insert(name.to_string());
         }
         // captureValueRefScope
@@ -711,6 +713,11 @@ impl<'t> Walker<'t> {
             "keyword_argument" => ("value", "value"),
             "pair" => ("value", "value"),
             "list" => ("list", ""),
+            // `return SomeClass` / `return handler` (#1478) — a single
+            // returned expression is a direct named child ('list' shape);
+            // tuple returns sit under expression_list and are not descended
+            // (mirrors PYTHON_SPEC).
+            "return_statement" => ("list", ""),
             _ => return,
         };
         if self.stack.is_empty() {