feat(search): PAPERLESS_SEARCH_LANGUAGE and PAPERLESS_ADVANCED_FUZZY_SEARCH_THRESHOLD settings

Add two new environment variables for Tantivy search backend:
- PAPERLESS_SEARCH_LANGUAGE: language code for stemming (empty string disables)
- PAPERLESS_ADVANCED_FUZZY_SEARCH_THRESHOLD: float threshold for fuzzy search blending (None disables)

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

src/paperless/settings/__init__.py

@@ -85,6 +85,13 @@ EMPTY_TRASH_DIR = (
 # threads.
 MEDIA_LOCK = MEDIA_ROOT / "media.lock"
 INDEX_DIR = DATA_DIR / "index"
+
+SEARCH_LANGUAGE: str = os.getenv("PAPERLESS_SEARCH_LANGUAGE", "")
+
+ADVANCED_FUZZY_SEARCH_THRESHOLD: float | None = get_float_from_env(
+    "PAPERLESS_ADVANCED_FUZZY_SEARCH_THRESHOLD",
+)
+
 MODEL_FILE = get_path_from_env(
     "PAPERLESS_MODEL_FILE",
     DATA_DIR / "classification_model.pickle",