feat(economic): add FAO Food Price Index panel (#2682)

* feat(economic): add FAO Food Price Index panel

Adds a new panel tracking the FAO Global Food Price Index (FFPI) for the
past 12 months, complementing existing consumer prices, fuel prices, and
Big Mac Index trackers.

- proto: GetFaoFoodPriceIndex RPC with 6-series response (Food, Cereals,
  Meat, Dairy, Oils, Sugar + MoM/YoY pct)
- seeder: seed-fao-food-price-index.mjs with 90-day TTL (3× monthly),
  isMain guard, parseVal NaN safety, correct 13-point slice
- handler/gateway: static tier RPC wired into economicHandler
- bootstrap/health: bootstrapped as SLOW_KEY; maxStaleMin=86400 (60 days)
- panel: SVG multi-line chart with 6 series, auto-scaled Y axis, headline
  with MoM/YoY indicators, info tooltip, bootstrap hydration
- CMD+K: panel:fao-food-price-index with fao/ffpi/food keywords
- Railway: fao-ffpi cron seeder service (0.5 vCPU, 0.5 GB, daily 08:45)
- locales: full en.json keys for panel UI strings
- ais-relay: faoFoodPriceIndex added to economic bootstrap context

* fix(economic): add faoFoodPriceIndex to cache-keys.ts BOOTSTRAP_CACHE_KEYS and BOOTSTRAP_TIERS

* fix(economic): correct cron comment in fao seeder to reflect daily schedule

docs/api/EconomicService.openapi.yaml

@@ -702,6 +702,32 @@ paths:
                         application/json:
                             schema:
                                 $ref: '#/components/schemas/Error'
+    /api/economic/v1/get-fao-food-price-index:
+        get:
+            tags:
+                - EconomicService
+            summary: GetFaoFoodPriceIndex
+            description: GetFaoFoodPriceIndex retrieves the FAO Food Price Index for the past 12 months.
+            operationId: GetFaoFoodPriceIndex
+            responses:
+                "200":
+                    description: Successful response
+                    content:
+                        application/json:
+                            schema:
+                                $ref: '#/components/schemas/GetFaoFoodPriceIndexResponse'
+                "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:
@@ -1919,3 +1945,46 @@ components:
                     format: double
                 missing:
                     type: boolean
+        GetFaoFoodPriceIndexRequest:
+            type: object
+        GetFaoFoodPriceIndexResponse:
+            type: object
+            properties:
+                points:
+                    type: array
+                    items:
+                        $ref: '#/components/schemas/FaoFoodPricePoint'
+                fetchedAt:
+                    type: string
+                currentFfpi:
+                    type: number
+                    format: double
+                momPct:
+                    type: number
+                    format: double
+                yoyPct:
+                    type: number
+                    format: double
+        FaoFoodPricePoint:
+            type: object
+            properties:
+                date:
+                    type: string
+                ffpi:
+                    type: number
+                    format: double
+                meat:
+                    type: number
+                    format: double
+                dairy:
+                    type: number
+                    format: double
+                cereals:
+                    type: number
+                    format: double
+                oils:
+                    type: number
+                    format: double
+                sugar:
+                    type: number
+                    format: double