feat(search): thread lang through NlSearchRequest → controller → NlQueryParserService → NlpClient

- NlSearchRequest gains @NotBlank @Pattern(regexp="de|en|es") lang field
- NlSearchController passes request.lang() to service
- NlQueryParserService.search signature: (String, String, Pageable); renames ollamaClient→nlpClient; removes redundant length guard (Bean Validation is enforcement point)
- application.yaml: replaces app.ollama.* with app.nlp.base-url; application-dev.yaml: points to localhost:8001
- frontend/documents/+page.svelte: sends lang: languageTag() in POST body

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

backend/src/main/resources/application.yaml

@@ -130,13 +130,8 @@ app:
     # The loader maps columns by header name — no positional indices (see ADR-025).
     dir: ${IMPORT_DIR:/import}
 
-  ollama:
-    base-url: http://ollama:11434
-    model: qwen2.5:7b-instruct-q4_K_M
-    # CPU inference: ~18s warm. Higher ceiling absorbs the cold model load on the
-    # first query after an Ollama (re)start before OLLAMA_KEEP_ALIVE pins it.
-    timeout-seconds: 60
-    health-check-timeout-seconds: 2
+  nlp:
+    base-url: http://nlp-service:8001
 
   nl-search:
     rate-limit: