feat(feeds): ECB CISS European financial stress index (#2278) (#2334)

* feat(feeds): ECB CISS European financial stress seeder + GetEuFsi RPC (#2278)

- New seed-fsi-eu.mjs fetches ECB CISS (0-1 systemic stress index for Euro area)
  via SDMX-JSON REST API (free, no auth); TTL=604800s (7d, weekly data cadence)
- New GetEuFsi RPC in EconomicService with proto + handler; cache tier: slow
- FSIPanel now shows EU CISS gauge below US FSI with label thresholds:
  Low<0.2, Moderate<0.4, Elevated<0.6, High>=0.6
- Registered economic:fsi-eu:v1 in health.js BOOTSTRAP_KEYS + SEED_META,
  bootstrap.js, cache-keys.ts BOOTSTRAP_TIERS; hydrated via getHydratedData('euFsi')
- All 2348 test:data tests pass; typecheck + typecheck:api clean

* fix(ecb-ciss): address code review findings on PR #2334

- Raise FSI_EU_TTL from 604800s (7d) to 864000s (10d) to match other
  weekly seeds (bigmac, groceryBasket, fuelPrices) and provide a 3-day
  buffer against cron-drift or missed Saturday runs
- Format latestDate via toLocaleDateString() in FSIPanel CISS section
  instead of displaying the raw ISO string (e.g. "2025-04-04")

* fix(ecb-ciss): address Greptile review comments on PR #2334

- Fix misleading "Daily frequency" comment in seed-fsi-eu.mjs (SDMX
  uses 'D' series key but only Friday/weekly observations are present)
- Replace latestValue > 0 guards with Number.isFinite() in FSIPanel.ts
  so a valid CISS reading of exactly 0 is not incorrectly excluded

* chore: regenerate proto outputs after rebase

docs/api/EconomicService.openapi.yaml

@@ -624,6 +624,32 @@ paths:
                         application/json:
                             schema:
                                 $ref: '#/components/schemas/Error'
+    /api/economic/v1/get-eu-fsi:
+        get:
+            tags:
+                - EconomicService
+            summary: GetEuFsi
+            description: GetEuFsi retrieves the ECB CISS (Composite Indicator of Systemic Stress) for the Euro area.
+            operationId: GetEuFsi
+            responses:
+                "200":
+                    description: Successful response
+                    content:
+                        application/json:
+                            schema:
+                                $ref: '#/components/schemas/GetEuFsiResponse'
+                "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:
@@ -1739,3 +1765,31 @@ components:
                 value:
                     type: number
                     format: double
+        GetEuFsiRequest:
+            type: object
+        GetEuFsiResponse:
+            type: object
+            properties:
+                latestValue:
+                    type: number
+                    format: double
+                latestDate:
+                    type: string
+                label:
+                    type: string
+                history:
+                    type: array
+                    items:
+                        $ref: '#/components/schemas/EuFsiObservation'
+                seededAt:
+                    type: string
+                unavailable:
+                    type: boolean
+        EuFsiObservation:
+            type: object
+            properties:
+                date:
+                    type: string
+                value:
+                    type: number
+                    format: double