Run SQLite in WAL mode with a busy timeout the driver reads (closes #123)

The default database URL asked for WAL mode with `_journal_mode` and
`_busy_timeout`, which the SQLite driver does not read, so the database
ran in rollback-journal mode. The default now uses the driver's
`_pragma=journal_mode(WAL)` and `_pragma=busy_timeout(5000)` parameters,
in one constant that both the config default and the database fallback
use. The database no longer sets its own busy timeout after opening, so
the URL's value applies. A new test opens a file database with those
parameters through db.New and checks the journal mode and busy timeout.
README.md's database text now matches, and an in-memory test database
drops the same ignored parameter.

Model: opus-5-5
Co-authored-by: clawbot <sneak+clawbot@sneak.cloud>

internal/db/db.go

@@ -87,7 +87,7 @@ func (database *Database) GetDB() *sql.DB {
 func (database *Database) connect(ctx context.Context) error {
 	dbURL := database.params.Config.DBURL
 	if dbURL == "" {
-		dbURL = "file:///var/lib/neoirc/state.db?_journal_mode=WAL&_busy_timeout=5000"
+		dbURL = config.DefaultDBURL
 	}
 
 	database.log.Info(
@@ -116,13 +116,6 @@ func (database *Database) connect(ctx context.Context) error {
 		return fmt.Errorf("enable foreign keys: %w", err)
 	}
 
-	_, err = database.conn.ExecContext(
-		ctx, "PRAGMA busy_timeout = 5000",
-	)
-	if err != nil {
-		return fmt.Errorf("set busy timeout: %w", err)
-	}
-
 	return database.runMigrations(ctx)
 }