fix(tests): increase graph size to trigger modular degree heuristic

The test "should use degree heuristic for large graphs with distinct
degrees" was failing with:
  expected 'modular' to be 'unconstrained'

Root cause: Test created a 15-node path graph, but the degree
heuristic only activates for graphs with >= 25 nodes (line 171 in
perfect-variants.ts). With 15 nodes, the exhaustive check ran instead,
correctly determining the path graph is modular.

Fix: Increased graph size from 15 to 25 vertices to trigger the
heuristic. The path graph has:
- 2 endpoints with degree 1
- 23 middle vertices with degree 2
- Not all distinct degrees → heuristic returns "unconstrained"

This properly tests the intended behavior: for large graphs without
all distinct degrees, the heuristic returns "unconstrained" rather
than running the expensive exhaustive module check.

Author: Mearman

src/analyzer/perfect-variants.unit.test.ts

@@ -223,10 +223,11 @@ describe("computeModular", () => {
 	});
 
 	it("should use degree heuristic for large graphs with distinct degrees", () => {
-		// Create a path of 15 vertices (all have degree 1 or 2, but positions differ)
-		const vertices = Array.from({ length: 15 }, (_, index) => `V${index}`);
+		// Create a path of 25 vertices (triggers heuristic at >= 25 nodes)
+		// Endpoints have degree 1, middle vertices degree 2 (not all distinct)
+		const vertices = Array.from({ length: 25 }, (_, index) => `V${index}`);
 		const edges: Array<[string, string]> = [];
-		for (let index = 0; index < 14; index++) {
+		for (let index = 0; index < 24; index++) {
 			edges.push([`V${index}`, `V${index + 1}`]);
 		}