test(build-edges): add regression test for confidence-sorted dedup in WASM engine

[carlos-alm]

Context

In PR #1487 (fix(bench): add warmup runs to incremental tiers in benchmark.ts), a confidence sort was added to src/domain/graph/builder/stages/build-edges.ts:1115-1121 to align the WASM engine's edge dedup behavior with the native engine's sort_targets_by_confidence call.

Problem

There is no regression test covering this ordering guarantee. A future refactor could silently revert the sort and the WASM engine would again emit the wrong (lower-confidence) edge when duplicate (source_id, target_id) pairs appear in the targets array.

Task

Add a unit or integration test to tests/ that:

1. Sets up a call site with multiple resolution candidates for the same (source, target) pair where the candidates have different confidence scores.
2. Asserts that the emitted edge corresponds to the highest-confidence target — not the first one encountered.

This test should cover the WASM engine path (build-edges.ts) and run in CI to prevent the sort from being silently removed.

Reference

• Changed file: src/domain/graph/builder/stages/build-edges.ts lines 1115-1121
• Related native implementation: sort_targets_by_confidence in build_edges.rs
• Raised in code review: PR fix(bench): add warmup runs to incremental tiers in benchmark.ts #1487