fix: ensure count is never null in GET /refractor/cards (#182)

Peewee's .count() on a complex multi-join query can return None when the
result wrapper yields an empty cursor for a 0-row result set.  Guard with
`or 0` so the response contract (count is always an integer) is upheld.

Note: tier values outside 0–4 already return 422 via FastAPI's ge/le
constraints on the tier parameter, so the reproduced scenario
(tier=99 → count: null) is also covered by validation.

Closes #182

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

CLAUDE.md

@@ -31,7 +31,7 @@ docker build -t paper-dynasty-db .                          # Build image
 | **URL** | pddev.manticorum.com | pd.manticorum.com |
 | **Host** | `ssh pd-database` | `ssh akamai` → `/root/container-data/paper-dynasty` |
 | **API container** | `dev_pd_database` | `pd_api` |
-| **PostgreSQL** | `pd_postgres` (port 5432) | `pd_postgres` |
+| **PostgreSQL** | `sba_postgres` / `paperdynasty_dev` / `sba_admin` | `pd_postgres` / `pd_master` |
 | **Adminer** | port 8081 | — |
 | **API port** | 816 | 815 |
 | **Image** | `manticorum67/paper-dynasty-database` | `manticorum67/paper-dynasty-database` |

app/routers_v2/refractor.py

@@ -211,7 +211,7 @@ async def list_card_states(
     if evaluated_only:
         query = query.where(RefractorCardState.last_evaluated_at.is_null(False))
 
-    total = query.count()
+    total = query.count() or 0
     items = []
     for state in query.offset(offset).limit(limit):
         player_name = None