fix(extraction): record instantiates for C++ stack/brace construction (#1035)

[colbymchenry]

Fixes #1035.

Problem

instantiates edges came only from heap new Calculator(0) (a new_expression) and copy-init Calculator c = Calculator(0) (a call_expression). Stack direct-init Calculator calc(0) and brace-init Widget w{1, 2} parse as a declaration whose constructor arguments hang directly off the declarator as an argument_list / initializer_list — there's no call/new node — so the function-body walker saw no constructor invocation and emitted no edge. A function that built objects with the ordinary stack syntax looked like it didn't construct them, and the dependency was missing from impact / callers.

Fix

In the body walker, a C++ declaration that is a stack/brace construction now reuses extractInstantiation (a declaration's type field is the constructed class name, and extractInstantiation already strips template args / namespace and emits the instantiates ref). Gated by isCppStackConstruction, which requires both:

• a class-like type (type_identifier / template_type / qualified_identifier) — so int x(0) (primitive) and auto z = … (handled via its own call_expression) are excluded; and
• a declarator carrying constructor args (argument_list / initializer_list) — so default construction Calculator c; and the most-vexing-parse Calculator c(); (a function declaration) are excluded.

The edge targets the class node, not the same-named constructor method. Template/namespace stripping is inherited: std::vector<int> v(10) → vector, ns::Widget w(0) → Widget.

Tests / verification

• 5 new tests under (#1035): 4 extraction (direct/brace-init emit the ref, template/namespace strip, negatives, multi-declarator) + 1 end-to-end resolution (instantiates resolves to the class; heap still works; primitives/default don't).
• Full extraction + resolution + graph suites → 536 passing, no regressions. Build clean.

Out of scope

Copy-init Calculator c = Calculator(0) records a calls edge to the constructor method rather than instantiates to the class — defensible either way, and this issue is specifically about the stack syntax. Can be a follow-up if we want it normalized.

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