Add recon form fingerprint library and SSRF canary mode.

Score crawl inputs by SSRF-prone field names and register ping-back canaries for operator paste confirmation.

server/internal/db/recon_canary_test.go

@@ -0,0 +1,16 @@
+package db
+
+import "testing"
+
+func TestReconSSRfCanaryInsertAndHit(t *testing.T) {
+	d, err := New(t.TempDir())
+	if err != nil { t.Fatal(err) }
+	t.Cleanup(func() { _ = d.Close() })
+	if err := d.InsertReconSSRfCanary("c1", "lab", "https://x/recon/ping/c1", "u", "i"); err != nil { t.Fatal(err) }
+	info, err := d.GetReconSSRfCanary("c1")
+	if err != nil || info.Status != "pending" { t.Fatal(info, err) }
+	hit, err := d.MarkReconSSRfCanaryHit("c1")
+	if err != nil || !hit { t.Fatal(hit, err) }
+	info, _ = d.GetReconSSRfCanary("c1")
+	if info.Status != "confirmed" || info.HitAt == nil { t.Fatal(info) }
+}