fix: survive junk RID dam values — widen storage_pct, bound inserts

Dam 100602 reports 87798% storage on some days, overflowing
NUMERIC(6,2) and discarding the entire 33-dam daily batch. storage_pct
is now NUMERIC(8,2) (auto-migrated on connect for existing Postgres/
MySQL tables) and every measure column is bounds-checked before insert
so out-of-capacity junk becomes NULL instead of a batch-killing error.
Rerunning the backfill repairs the days the overflow skipped.

tests/test_rid_reservoir.py

@@ -123,6 +123,35 @@ class TestStore:
     def test_save_empty(self, store):
         assert store.save([]) == 0
 
+    def test_junk_source_values_are_nulled_not_fatal(self, store):
+        # Real junk from 2019-01-05: dam 100602 reported 87798% storage,
+        # which overflowed NUMERIC(6,2) and discarded the whole 33-dam batch.
+        payload = _dams_payload()
+        payload["regions"][0]["dams"].append(
+            {
+                "DAM_ID": "100602",
+                "DAM_Name": "junk",
+                "DMD_Date": "2026-08-13",
+                "DMD_QUse": "343292.00",
+                "PERCENT_DMD_QUse": "87798.00",
+                "DMD_Inflow": "0.59",
+                "DMD_Outflow": "1e12",  # beyond NUMERIC(10,2) -> NULL
+            }
+        )
+        assert store.save(parse_dam_records(payload)) == 3
+        from sqlalchemy import text
+
+        with store.engine.begin() as conn:
+            row = conn.execute(
+                text(
+                    "SELECT storage_mcm, storage_pct, outflow_mcm "
+                    "FROM rid_reservoir_daily WHERE dam_id = '100602'"
+                )
+            ).fetchone()
+        assert float(row[0]) == 343292.00  # fits NUMERIC(10,2), kept raw
+        assert float(row[1]) == 87798.00  # fits widened NUMERIC(8,2)
+        assert row[2] is None  # beyond capacity -> NULL, batch survives
+
     def test_present_dates(self, store):
         lo, hi = datetime.date(2026, 8, 1), datetime.date(2026, 8, 31)
         assert store.present_dates(lo, hi) == set()