feat: add hide unknown locations toggle in site settings

Adds toggle in Data & Privacy > Filtering section to exclude entries
where geographic data could not be resolved from location stats.

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

lib/api/sites.ts

@@ -21,6 +21,8 @@ export interface Site {
   enable_performance_insights?: boolean
   // Bot and noise filtering
   filter_bots?: boolean
+  // Hide unknown locations from stats
+  hide_unknown_locations?: boolean
   // Data retention (months); 0 = keep forever
   data_retention_months?: number
   created_at: string
@@ -49,6 +51,8 @@ export interface UpdateSiteRequest {
   enable_performance_insights?: boolean
   // Bot and noise filtering
   filter_bots?: boolean
+  // Hide unknown locations from stats
+  hide_unknown_locations?: boolean
   // Data retention (months); 0 = keep forever
   data_retention_months?: number
 }