fix(webapp): include "not_findable" in the admin pricing-unit options

So the edit form has a matching option for models the research pipeline
marks not_findable, instead of a controlled select with no match.

Author: ericallam

apps/webapp/app/routes/admin.llm-models.$modelId.tsx

@@ -445,7 +445,7 @@ type TierData = {
   prices: Record<string, number>;
 };
 
-const PRICING_UNITS = ["tokens", "characters", "images", "minutes", "requests", "free"];
+const PRICING_UNITS = ["tokens", "characters", "images", "minutes", "requests", "free", "not_findable"];
 
 const COMMON_USAGE_TYPES = [
   "input",

apps/webapp/app/routes/admin.llm-models.new.tsx

@@ -386,7 +386,7 @@ type TierData = {
   prices: Record<string, number>;
 };
 
-const PRICING_UNITS = ["tokens", "characters", "images", "minutes", "requests", "free"];
+const PRICING_UNITS = ["tokens", "characters", "images", "minutes", "requests", "free", "not_findable"];
 
 const COMMON_USAGE_TYPES = [
   "input",