Add HowLongToBeat estimates to game cards

- Fetch HLTB main/extra/completionist hours when a game item is saved
- Re-fetch only when name or category changes on edit
- Steam imports also fetch HLTB for each selected game
- Cards show compact HLTB row: "HLTB: 40h · +extra 60h · 100% 100h"
- Edit form shows HLTB breakdown as a hint next to Total hours field

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

requirements.txt

@@ -4,3 +4,4 @@ whitenoise>=6.6
 requests>=2.31
 beautifulsoup4>=4.12
 deep-translator>=1.11
+howlongtobeatpy>=2.0