fix(database): cast count(*)::int in get_db_status to match i32 field

count(*) returns bigint (int8) in PostgreSQL, but the result was read as
i32 via conn_row.get(0). tokio-postgres's FromSql<i32> rejects an int8
column, so get_db_status panicked at runtime with
'error deserializing column 0' (HTTP 500).

Cast count(*)::int to int4, matching the adjacent setting::int column
and the total_connections/max_connections i32 struct fields. No other
queries in the file are affected: reltuples is already ::bigint -> i64,
size columns are native bigint -> i64, and system_status.rs reads its
count(*) as i64 correctly.

src/api/database/status.rs

@@ -89,10 +89,12 @@ pub async fn get_db_status() -> Result<DbStatus, ServerFnError> {
             .map_err(AppError::query)?
             .get(0);
 
-        // 当前库连接数 + 全局最大连接数
+        // 当前库连接数 + 全局最大连接数。
+        // count(*) 原生返回 bigint(int8)，与下方 setting::int 一并显式转 int4，
+        // 以匹配 total_connections/max_connections 的 i32 类型（否则 FromSql 反序列化失败）。
         let conn_row = client
             .query_one(
-                "SELECT count(*), \
+                "SELECT count(*)::int, \
                  (SELECT setting::int FROM pg_settings WHERE name = 'max_connections') \
                  FROM pg_stat_activity WHERE datname = current_database()",
                 &[],