feat(feeds): US Natural Gas Storage weekly seeder (EIA NW2_EPG0_SWO_R48_BCF) (#2353)

* feat(feeds): US Natural Gas Storage seeder via EIA (NW2_EPG0_SWO_R48_BCF)

Adds weekly EIA natural gas working gas storage for the Lower-48 states
(series NW2_EPG0_SWO_R48_BCF, in Bcf), mirroring the crude inventories
pattern exactly. Companion dataset to EU gas storage (GIE AGSI+).

- proto: GetNatGasStorage RPC + NatGasStorageWeek message
- seed-economy.mjs: fetchNatGasStorage() in Promise.allSettled, writes
  economic:nat-gas-storage:v1 with 21-day TTL (3x weekly cadence)
- server handler: getNatGasStorage reads seeded key from Redis
- gateway: /api/economic/v1/get-nat-gas-storage → static tier
- health.js: BOOTSTRAP_KEYS + SEED_META (14-day maxStaleMin)
- bootstrap.js: KEYS + SLOW_KEYS
- cache-keys.ts: BOOTSTRAP_CACHE_KEYS + BOOTSTRAP_TIERS (slow)

* feat(feeds): add fetchNatGasStorageRpc consumer in economic service

Adds getHydratedData('natGasStorage') consumer required by bootstrap
key registry test, plus circuit breaker and RPC wrapper mirroring
fetchCrudeInventoriesRpc pattern.

docs/api/EconomicService.openapi.yaml

@@ -520,6 +520,32 @@ paths:
                         application/json:
                             schema:
                                 $ref: '#/components/schemas/Error'
+    /api/economic/v1/get-nat-gas-storage:
+        get:
+            tags:
+                - EconomicService
+            summary: GetNatGasStorage
+            description: GetNatGasStorage retrieves the 8 most recent weeks of US natural gas working gas storage from EIA (NW2_EPG0_SWO_R48_BCF).
+            operationId: GetNatGasStorage
+            responses:
+                "200":
+                    description: Successful response
+                    content:
+                        application/json:
+                            schema:
+                                $ref: '#/components/schemas/GetNatGasStorageResponse'
+                "400":
+                    description: Validation error
+                    content:
+                        application/json:
+                            schema:
+                                $ref: '#/components/schemas/ValidationError'
+                default:
+                    description: Error response
+                    content:
+                        application/json:
+                            schema:
+                                $ref: '#/components/schemas/Error'
     /api/economic/v1/get-ecb-fx-rates:
         get:
             tags:
@@ -1586,6 +1612,37 @@ components:
                         Week-over-week change in millions of barrels. Positive = build (bearish), negative = draw (bullish).
                          Absent for the oldest week when no prior week is available for comparison.
             description: CrudeInventoryWeek represents one week of US crude oil stockpile data from EIA WCRSTUS1.
+        GetNatGasStorageRequest:
+            type: object
+            description: GetNatGasStorageRequest is the request message for GetNatGasStorage.
+        GetNatGasStorageResponse:
+            type: object
+            properties:
+                weeks:
+                    type: array
+                    items:
+                        $ref: '#/components/schemas/NatGasStorageWeek'
+                latestPeriod:
+                    type: string
+                    description: Timestamp of the most recent EIA data point (ISO 8601).
+            description: GetNatGasStorageResponse contains the 8 most recent weeks of US natural gas storage data.
+        NatGasStorageWeek:
+            type: object
+            properties:
+                period:
+                    type: string
+                    description: ISO week period (YYYY-MM-DD, Monday of the EIA report week).
+                storBcf:
+                    type: number
+                    format: double
+                    description: Working gas in underground storage, Lower-48 States, in Bcf.
+                weeklyChangeBcf:
+                    type: number
+                    format: double
+                    description: |-
+                        Week-over-week change in Bcf. Positive = build (bearish for gas prices), negative = draw (bullish).
+                         Absent for the oldest week when no prior week is available for comparison.
+            description: NatGasStorageWeek represents one week of US natural gas working gas storage data from EIA.
         GetEcbFxRatesRequest:
             type: object
             description: GetEcbFxRatesRequest is empty; returns all tracked EUR pairs.