fix: increase vector sync wait timeout to prevent sampling test timeouts in CI

Extract reusable wait_for_vector_sync() helper with 90s max_wait (up from
30s) to handle slow single-worker processing in CI. Increase processor
workers to 2 for the mcp service to parallelize note indexing.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

docker-compose.yml

@@ -92,7 +92,7 @@ services:
       # Semantic search configuration (ADR-007, ADR-021)
       - ENABLE_SEMANTIC_SEARCH=true
       - VECTOR_SYNC_SCAN_INTERVAL=5
-      - VECTOR_SYNC_PROCESSOR_WORKERS=1
+      - VECTOR_SYNC_PROCESSOR_WORKERS=2
 
       #- LOG_FORMAT=json