fix: code review cleanup - schema sync, type safety, null handling

- Sync KnowledgeLink schema with migration (add displayText, positionStart, positionEnd, resolved)
- Make targetId optional to support unresolved links
- Fix null handling in graph.service.ts (skip unresolved links)
- Add explicit types to frontend components (remove implicit any)
- Remove unused WikiLink import
- Add null-safe statusInfo check in EntryCard

apps/api/prisma/schema.prisma

@@ -750,18 +750,22 @@ model KnowledgeLink {
   sourceId String         @map("source_id") @db.Uuid
   source   KnowledgeEntry @relation("SourceEntry", fields: [sourceId], references: [id], onDelete: Cascade)
 
-  targetId String         @map("target_id") @db.Uuid
-  target   KnowledgeEntry @relation("TargetEntry", fields: [targetId], references: [id], onDelete: Cascade)
+  targetId String?        @map("target_id") @db.Uuid
+  target   KnowledgeEntry? @relation("TargetEntry", fields: [targetId], references: [id], onDelete: Cascade)
 
   // Link metadata
-  linkText String  @map("link_text")
-  context  String?
+  linkText      String  @map("link_text")
+  displayText   String  @map("display_text")
+  positionStart Int     @map("position_start")
+  positionEnd   Int     @map("position_end")
+  resolved      Boolean @default(false)
+  context       String?
 
   createdAt DateTime @default(now()) @map("created_at") @db.Timestamptz
 
-  @@unique([sourceId, targetId])
   @@index([sourceId])
   @@index([targetId])
+  @@index([sourceId, resolved])
   @@map("knowledge_links")
 }