feat: remove EXTERNAL_MARKET result type entirely

All external market properties now surface as VERIFIED_PORTFOLIO.
Removes the type from enums, domain types, mock data, matching engine,
components, hooks, and tests — zero user-visible distinction remains.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/lib/constants.ts

@@ -69,7 +69,6 @@ export const ASSET_TYPE_LABELS: Record<string, string> = {
 // Result type display labels
 export const RESULT_TYPE_LABELS: Record<string, string> = {
   VERIFIED_PORTFOLIO:  'Plattform',
-  EXTERNAL_MARKET:     'Plattform',
   MAISON_WORK:         'Maison Work',
   FUTURE_AVAILABILITY: 'Zukunftssignal',
 }