fix(api): POST /v1/search names unknown providers instead of opaque 400 (#10849)

v1SearchSchema.provider was a hard-coded z.enum that rejected any id outside
its list before the route's own resolveSearchProvider() check ever ran,
so unknown/short-alias provider ids (grok, brave, serper, ...) always
surfaced a generic "Invalid request" instead of the informative
"Unknown search provider: <id>" message. Relax the schema to a free-form
string and let resolveSearchProvider() own runtime validation (as it
already did for ids that passed the enum). Also extend
SEARCH_PROVIDER_ALIASES with short-form aliases mirroring the existing
jina/jina-ai pattern (brave, serper, perplexity, exa, tavily, google-pse,
linkup, ollama, searchapi, youcom, searxng, zai, duckduckgo), and surface
the first Zod validation issue's field name instead of the generic
message for other still-invalid fields (e.g. search_type).

src/app/api/v1/search/route.ts

@@ -19,7 +19,11 @@ import * as log from "@/sse/utils/logger";
 import { toJsonErrorPayload } from "@/shared/utils/upstreamError";
 import { enforceApiKeyPolicy } from "@/shared/utils/apiKeyPolicy";
 import { v1SearchSchema } from "@/shared/validation/schemas";
-import { isValidationFailure, validateBody } from "@/shared/validation/helpers";
+import {
+  formatValidationMessage,
+  isValidationFailure,
+  validateBody,
+} from "@/shared/validation/helpers";
 import { recordCost } from "@/domain/costRules";
 import {
   computeCacheKey,
@@ -120,7 +124,7 @@ async function postHandler(request: Request, context: unknown) {
 
   const validation = validateBody(v1SearchSchema, rawBody);
   if (isValidationFailure(validation)) {
-    return errorResponse(HTTP_STATUS.BAD_REQUEST, validation.error.message);
+    return errorResponse(HTTP_STATUS.BAD_REQUEST, formatValidationMessage(validation.error));
   }
   const body = validation.data;