Fix TypeError when revision_count is stored as TEXT

The previous schema migration added revision_count as TEXT. SQLite stores
the default as TEXT, but the app does integer arithmetic on it, causing:

  TypeError: unsupported operand type(s) for -: 'int' and 'str'

- init_db() now adds revision_count as INTEGER.
- app.py casts revision_count to int in play() and revise() and when
  incrementing in revise(), so existing TEXT values also work.

Bump version 0.4.2 -> 0.4.3.

models.py

@@ -117,8 +117,9 @@ def init_db():
         existing = {r['name'] for r in db.execute(f"PRAGMA table_info({table})")}
         for col in columns:
             if col not in existing:
-                # Use a safe default type; NULLable for all current optional columns.
-                db.execute(f'ALTER TABLE {table} ADD COLUMN {col} TEXT')
+                # revision_count must be INTEGER so arithmetic in app.py works.
+                col_type = 'INTEGER' if col == 'revision_count' else 'TEXT'
+                db.execute(f'ALTER TABLE {table} ADD COLUMN {col} {col_type}')
     db.commit()
     db.close()