Add hydro security sweep state (2026-04-17)

No CRITICAL or HIGH severity issues found in hydro module.
MEDIUM findings: unbounded queue allocation (h*w*8 bytes in BFS
kernels), division by cellsize without zero-check, some secondary
inputs not validated with _validate_raster.

Author: brendancol

.claude/sweep-security-state.json

@@ -0,0 +1,10 @@
+{
+  "inspections": {
+    "hydro": {
+      "last_inspected": "2026-04-17",
+      "issue": null,
+      "severity_max": "MEDIUM",
+      "categories_found": [1, 3, 6]
+    }
+  }
+}