feat(detection-core): unique-declaration member-call binding (8.2 final gated round step 1-2)

x.method() with a variable receiver binds complete iff exactly one same-name
method declaration exists repository-wide; collisions stay a finite candidate
set (receiver_type_unknown) and module-level functions never bind. Authorized
by maintainer strategy-review 2026-10-31; gated by dev-pool FA non-regression.

tests/test_obligation_summaries.py

@@ -540,6 +540,10 @@ JAVA_AUDITOR = """class Auditor {
     public void check() {
     }
 }
+class Gate {
+    public void check() {
+    }
+}
 """