fix(cpp): resolve calls through singletons/factories/chained getters (#645) (#742)

A C++ method call whose receiver is another call's result — `Foo::instance().bar()`,
`WidgetFactory::create().draw()`, `openSession()->run()`, or the same stored in an
`auto` local first — lost the receiver's type during extraction. The callee degraded
to a bare method name, so when two classes shared a method name the call silently
resolved to whichever was indexed first (or not at all), corrupting callers / impact /
trace with a plausible-but-wrong edge.

Three parts:
- Capture C++ return types (new nodes.return_type column, schema v5): the
  function_definition's `type` field, normalized — smart-pointer pointee unwrapped,
  void/primitives dropped.
- Preserve the inner-call receiver in extraction: a C/C++ field_expression whose
  receiver is itself a call is encoded `inner().method` instead of dropping to the
  bare name. Other languages keep the existing behavior.
- New resolution strategy (matchCppCallChain): infer the receiver's class from the
  inner call's return type, then resolve AND validate the method on it. Handles
  singletons/accessors, factories returning a different type, free-function
  factories, make_unique/make_shared/new/direct construction, single-level member
  chains, and namespace-qualified inner calls. A wrong inference yields no edge,
  never a wrong one.

EXTRACTION_VERSION 2->3 (re-index to populate return types).

Validated on the issue repro + spdlog: node count stable (no explosion),
deterministic, and ~100 pre-existing wrong `.size()`-style edges removed.

Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/extraction/tree-sitter-types.ts

@@ -205,6 +205,15 @@ export interface LanguageExtractor {
    */
   getReceiverType?: (node: SyntaxNode, source: string) => string | undefined;
 
+  /**
+   * Extract a function/method's normalized return type name (bare class name,
+   * smart-pointer pointee unwrapped), stored on the node as `returnType`. Used
+   * by C/C++ so resolution can infer a chained receiver's type from what the
+   * inner call returns (`Foo::instance().bar()` → resolve `bar` on `Foo`,
+   * issue #645). Return undefined for primitives / void / constructors.
+   */
+  getReturnType?: (node: SyntaxNode, source: string) => string | undefined;
+
   /**
    * Resolve the actual node kind for a type alias declaration.
    * Used by Go where `type_spec` is the named declaration wrapper for structs/interfaces: