perf(ai-scanner): drop confidence scoring to simplify AI menu import

Removes the per-item confidence field end to end (prompt, extraction
parsing, ai_import_items writes, API responses, low-confidence badge
in the mobile review screen). ai_import_items.confidence column is
left in place but unused (nullable, no destructive migration).

packages/shared/src/types.ts

@@ -78,7 +78,6 @@ export interface AiImportItem {
   itemName: string;
   description: string | null;
   price: number | null;
-  confidence: number | null;
 }
 
 export interface AiExtractedItem {
@@ -86,7 +85,6 @@ export interface AiExtractedItem {
   name: string;
   description?: string | null;
   price: number;
-  confidence: number;
 }
 
 export interface AiExtractedCategory {
@@ -101,7 +99,6 @@ export interface AiImportResponse {
   model: string | null;
   categories: AiExtractedCategory[];
   totalItems: number;
-  lowConfidenceCount: number;
 }
 
 export interface AiImportApplyPayload {