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/domain/pipeline.ts

@@ -5,7 +5,7 @@ export interface PipelineItem {
   title: string
   location: string
   matchScore: number
-  resultType: 'VERIFIED_PORTFOLIO' | 'EXTERNAL_MARKET' | 'MAISON_WORK' | 'FUTURE_AVAILABILITY'
+  resultType: 'VERIFIED_PORTFOLIO' | 'MAISON_WORK' | 'FUTURE_AVAILABILITY'
   stage: PipelineStage
   // Source match reference — used for navigating back to the detail page
   matchId?: string