fix(chat): decode pg_class.reltuples as f32 in sample_data probe

pg_class.reltuples is `real` (FLOAT4). Reading it as f64 via query_scalar made
the sample_data tool fail with a sqlx type-mismatch ("f64 (FLOAT8) is not
compatible with FLOAT4") before any rows were fetched. Decode as f32 and widen.

src-tauri/src/commands/chat_tools.rs

@@ -899,7 +899,9 @@ async fn build_sample_sql_postgres(
     limit: u32,
 ) -> TuskResult<String> {
     let pool = state.get_pool(connection_id).await?;
-    let reltuples: f64 = sqlx::query_scalar(
+    // pg_class.reltuples is `real` (FLOAT4); decode as f32 then widen — sqlx is
+    // strict and reading it directly as f64 fails with a type-mismatch error.
+    let reltuples: f64 = sqlx::query_scalar::<_, f32>(
         "SELECT c.reltuples FROM pg_class c JOIN pg_namespace n ON c.relnamespace = n.oid \
          WHERE n.nspname = $1 AND c.relname = $2",
     )
@@ -908,7 +910,7 @@ async fn build_sample_sql_postgres(
     .fetch_optional(&pool)
     .await
     .map_err(TuskError::Database)?
-    .unwrap_or(0.0);
+    .unwrap_or(0.0) as f64;
 
     let qualified = format!("{}.{}", escape_ident(schema), escape_ident(table));
     if reltuples > 0.0 {