feat: add fuzzysearch dependency for scanner engine

cmd/naviwatcher/fuzzy_smoke_test.go

@@ -0,0 +1,45 @@
+package main
+
+import (
+	"testing"
+
+	"github.com/lithammer/fuzzysearch/fuzzy"
+)
+
+// TestFuzzySmoke verifies the fuzzysearch dependency is importable and that
+// its ranking API behaves as the scanner engine will expect.
+//
+// Note: this library does NOT expose a `fuzzy.Ratio` (0-100) function as the
+// plan's Technical Details assumed. The relevant signal here is RankMatch,
+// which returns 0 for an exact match, a small positive distance for near
+// matches, and -1 when source is not a subsequence of target. Task 3 will
+// convert this into a normalized 0.0-1.0 similarity score.
+func TestFuzzySmoke(t *testing.T) {
+	// Exact match scores 0 (distance).
+	if got := fuzzy.RankMatch("the wall", "the wall"); got != 0 {
+		t.Errorf("expected RankMatch of identical strings to be 0, got %d", got)
+	}
+
+	// Similar strings score closer to 0 than dissimilar ones, and a real
+	// subsequence match returns a non-negative distance.
+	similar := fuzzy.RankMatch("the wall", "the wall remastered")
+	dissimilar := fuzzy.RankMatch("the wall", "completely different album")
+
+	if similar < 0 {
+		t.Errorf("expected similar to be a valid match (>=0), got %d", similar)
+	}
+	if dissimilar >= 0 {
+		t.Errorf("expected dissimilar to be a non-match (-1), got %d", dissimilar)
+	}
+	if dissimilar != -1 {
+		t.Errorf("expected dissimilar to be -1 (no subsequence match), got %d", dissimilar)
+	}
+
+	// A near match (valid, >=0) is preferable to a total miss (-1).
+	if similar < 0 {
+		t.Errorf("expected similar to be a valid match (>=0), got %d", similar)
+	}
+	if dissimilar != -1 {
+		t.Errorf("expected dissimilar to be a non-match (-1), got %d", dissimilar)
+	}
+}