feat(trade): add US Treasury customs revenue to Trade Policy panel (#1663)

* feat(trade): add US Treasury customs revenue to Trade Policy panel

US customs duties revenue spiked 4-5x under Trump tariffs (from
$7B/month to $27-31B/month) but the WTO tariff data only goes to
2024. Adds Treasury MTS data showing monthly customs revenue.

- Add GetCustomsRevenue RPC (proto, handler, cache tier)
- Add Treasury fetch to seed-supply-chain-trade.mjs (free API, no key)
- Add Revenue tab to TradePolicyPanel with FYTD YoY comparison
- Fix WTO gate: per-tab gating so Revenue works without WTO key
- Wire bootstrap hydration, health, seed-health tracking

* test(trade): add customs revenue feature tests

22 structural tests covering:
- Handler: raw key mode, empty-cache behavior, correct Redis key
- Seed: Treasury API URL, classification filter, timeout, row
  validation, amount conversion, sort order, seed-meta naming
- Panel: WTO gate fix (per-tab not panel-wide), revenue tab
  defaults when WTO key missing, dynamic FYTD comparison
- Client: no WTO feature gate, bootstrap hydration, type exports

* fix(trade): align FYTD comparison by fiscal month count

Prior FY comparison was filtering by calendar month, which compared
5 months of FY2026 (Oct-Feb) against only 2 months of FY2025
(Jan-Feb), inflating the YoY percentage. Now takes the first N
months of the prior FY matching the current FY month count.

* fix(trade): register treasury_revenue DataSourceId and localize revenue tab

- Add treasury_revenue to DataSourceId union type so freshness
  tracking actually works (was silently ignored)
- Register in data-freshness.ts source config + gap messages
- Add i18n keys: revenue tab label, empty state, unavailable banner
- Update infoTooltip to include Revenue tab description

* fix(trade): complete revenue tab localization

Use t() for all remaining hardcoded strings: footer source labels,
FYTD summary headline, prior-year comparison, and table column
headers. Wire the fytdLabel/vsPriorFy keys that were added but
not used.

* fix(test): update revenue source assertion for localized string

docs/api/TradeService.openapi.yaml

@@ -187,6 +187,32 @@ paths:
                         application/json:
                             schema:
                                 $ref: '#/components/schemas/Error'
+    /api/trade/v1/get-customs-revenue:
+        get:
+            tags:
+                - TradeService
+            summary: GetCustomsRevenue
+            description: Get US customs duties revenue (Treasury MTS data, seeded by Railway).
+            operationId: GetCustomsRevenue
+            responses:
+                "200":
+                    description: Successful response
+                    content:
+                        application/json:
+                            schema:
+                                $ref: '#/components/schemas/GetCustomsRevenueResponse'
+                "400":
+                    description: Validation error
+                    content:
+                        application/json:
+                            schema:
+                                $ref: '#/components/schemas/ValidationError'
+                default:
+                    description: Error response
+                    content:
+                        application/json:
+                            schema:
+                                $ref: '#/components/schemas/Error'
 components:
     schemas:
         Error:
@@ -459,3 +485,37 @@ components:
                     type: string
                     description: WTO source document URL (must be http/https protocol).
             description: SPS or TBT trade barrier notification.
+        GetCustomsRevenueRequest:
+            type: object
+        GetCustomsRevenueResponse:
+            type: object
+            properties:
+                months:
+                    type: array
+                    items:
+                        $ref: '#/components/schemas/CustomsRevenueMonth'
+                fetchedAt:
+                    type: string
+                upstreamUnavailable:
+                    type: boolean
+        CustomsRevenueMonth:
+            type: object
+            properties:
+                recordDate:
+                    type: string
+                fiscalYear:
+                    type: integer
+                    format: int32
+                calendarYear:
+                    type: integer
+                    format: int32
+                calendarMonth:
+                    type: integer
+                    format: int32
+                monthlyAmountBillions:
+                    type: number
+                    format: double
+                fytdAmountBillions:
+                    type: number
+                    format: double
+            description: Monthly US customs duties revenue from Treasury MTS data.