Fix: Hardcode Kaikki stats (COUNT on 6M rows took 100s, blocked server)

SELECT COUNT(*) FROM vocabulary_kaikki was 100+ seconds without index,
blocking the entire backend. Hardcoded to 6,271,749 / 24 languages.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

backend-lehrer/vocabulary/api.py

@@ -146,24 +146,13 @@ async def api_get_filters():
     tags = await get_all_tags()
     pos_list = await get_all_pos()
     total = await count_words()
-    # Kaikki stats
-    kaikki_total = 0
-    kaikki_langs = 0
-    try:
-        from vocabulary.db import get_pool
-        pool = await get_pool()
-        async with pool.acquire() as conn:
-            kaikki_total = await conn.fetchval("SELECT COUNT(*) FROM vocabulary_kaikki")
-            kaikki_langs = await conn.fetchval("SELECT COUNT(DISTINCT lang) FROM vocabulary_kaikki")
-    except Exception:
-        pass
-
+    # Kaikki stats (hardcoded to avoid slow COUNT on 6M rows)
     return {
         "tags": tags,
         "parts_of_speech": pos_list,
         "total_words": total,
-        "kaikki_total": kaikki_total,
-        "kaikki_languages": kaikki_langs,
+        "kaikki_total": 6271749,
+        "kaikki_languages": 24,
     }