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>

backlogger/hltb.py

@@ -0,0 +1,48 @@
+from howlongtobeatpy import HowLongToBeat
+
+
+def _h(val):
+    """Return float hours if valid, else None."""
+    try:
+        v = float(val)
+        return v if v > 0 else None
+    except (TypeError, ValueError):
+        return None
+
+
+def fetch(game_name):
+    """
+    Search HowLongToBeat for game_name.
+    Returns dict with keys 'main', 'extra', 'complete' (each float or None),
+    or None if nothing found / on any error.
+    """
+    try:
+        results = HowLongToBeat().search(game_name)
+    except Exception:
+        return None
+
+    if not results:
+        return None
+
+    best = max(results, key=lambda r: r.similarity)
+    if best.similarity < 0.4:
+        return None
+
+    return {
+        'main': _h(best.main_story),
+        'extra': _h(best.main_extra),
+        'complete': _h(best.completionist),
+    }
+
+
+def apply_to_item(item):
+    """Fetch HLTB data and save it onto item. Silently does nothing on failure."""
+    if item.category != 'games' or not item.name:
+        return
+    data = fetch(item.name)
+    if data is None:
+        return
+    item.hltb_main = data['main']
+    item.hltb_extra = data['extra']
+    item.hltb_complete = data['complete']
+    item.save(update_fields=['hltb_main', 'hltb_extra', 'hltb_complete'])