feat: improve generate sql template

1.Add parameter: GENERATE_SQL_QUERY_LIMIT_ENABLED (default value is True to control data return Limit 1000 rows)
2.Use different SQL example templates based on different data sources.

backend/templates/sql_examples/MySQL.yaml

@@ -0,0 +1,86 @@
+template:
+  quot_rule: |
+    <rule>
+      必须对数据库名、表名、字段名、别名外层加反引号（`）。
+      <note>
+        1. 点号（.）不能包含在反引号内，必须写成 `schema`.`table`
+        2. 当标识符为关键字、含特殊字符或需保留大小写时必须加反引号
+        3. MySQL 默认不区分大小写（Linux系统区分表名大小写）
+      </note>
+    </rule>
+
+  limit_rule: |
+    <rule>
+      行数限制使用标准SQL语法：
+      <note>
+        1. 标准写法：LIMIT [count]
+        2. 分页写法：LIMIT [offset], [count] 或 LIMIT [count] OFFSET [start]
+      </note>
+    </rule>
+
+  other_rule: |
+    <rule>必须为每个表生成别名（不加AS）</rule>
+    <rule>禁止使用星号(*)，必须明确字段名</rule>
+    <rule>中文/特殊字符字段需保留原名并添加英文别名</rule>
+    <rule>函数字段必须加别名</rule>
+    <rule>百分比显示为：CONCAT(ROUND(x*100,2),'%')</rule>
+    <rule>避免与MySQL关键字冲突（如`order`/`group`/`desc`）</rule>
+
+  basic_example: |
+    <basic-examples>
+      <intro>
+        📌 以下示例严格遵循<Rules>中的 MySQL 规范，展示符合要求的 SQL 写法与典型错误案例。
+        ⚠️ 注意：示例中的表名、字段名均为演示虚构，实际使用时需替换为用户提供的真实标识符。
+        🔍 重点观察：
+          1. 双引号包裹所有数据库对象的规范用法
+          2. 中英别名/百分比/函数等特殊字段的处理
+          3. 关键字冲突的规避方式
+      </intro>
+      <example>
+        <input>查询 test.orders 表的前100条订单（含中文字段和百分比）</input>
+        <output-bad>
+          SELECT * FROM test.orders LIMIT 100  -- 错误：使用星号
+          SELECT `订单ID`, `金额` FROM `test`.`orders` `t1` LIMIT 100  -- 错误：缺少英文别名
+          SELECT COUNT(`订单ID`) FROM `test`.`orders` `t1`  -- 错误：函数未加别名
+        </output-bad>
+        <output-good>
+          SELECT 
+            `t1`.`订单ID` AS `order_id`,
+            `t1`.`金额` AS `amount`,
+            COUNT(`t1`.`订单ID`) AS `total_orders`,
+            CONCAT(ROUND(`t1`.`折扣率` * 100, 2), '%') AS `discount_percent`
+          FROM `test`.`orders` `t1`
+          LIMIT 100
+        </output-good>
+      </example>
+
+      <example>
+        <input>统计用户表 public.users（含关键字字段desc）的活跃占比</input>
+        <output-bad>
+          SELECT desc, status FROM public.users  -- 错误：未处理关键字
+          SELECT `desc`, ROUND(active_ratio*100) FROM `public`.`users`  -- 错误：百分比格式错误
+        </output-bad>
+        <output-good>
+          SELECT 
+            `u`.`desc` AS `description`,
+            CONCAT(ROUND(`u`.`active_ratio` * 100, 2), '%') AS `active_percent`
+          FROM `public`.`users` `u`
+          WHERE `u`.`status` = 1
+          LIMIT 1000
+        </output-good>
+      </example>
+    </basic-examples>
+
+  example_engine: MySQL 8.0
+  example_answer_1: |
+    {"success":true,"sql":"SELECT `country` AS `country_name`, `continent` AS `continent_name`, `year` AS `year`, `gdp` AS `gdp_usd` FROM `Sample_Database`.`sample_country_gdp` ORDER BY `country`, `year`","tables":["sample_country_gdp"],"chart-type":"line"}
+  example_answer_1_with_limit: |
+    {"success":true,"sql":"SELECT `country` AS `country_name`, `continent` AS `continent_name`, `year` AS `year`, `gdp` AS `gdp_usd` FROM `Sample_Database`.`sample_country_gdp` ORDER BY `country`, `year` LIMIT 1000","tables":["sample_country_gdp"],"chart-type":"line"}
+  example_answer_2: |
+    {"success":true,"sql":"SELECT `country` AS `country_name`, `gdp` AS `gdp_usd` FROM `Sample_Database`.`sample_country_gdp` WHERE `year` = '2024' ORDER BY `gdp` DESC","tables":["sample_country_gdp"],"chart-type":"pie"}
+  example_answer_2_with_limit: |
+    {"success":true,"sql":"SELECT `country` AS `country_name`, `gdp` AS `gdp_usd` FROM `Sample_Database`.`sample_country_gdp` WHERE `year` = '2024' ORDER BY `gdp` DESC LIMIT 1000","tables":["sample_country_gdp"],"chart-type":"pie"}
+  example_answer_3: |
+    {"success":true,"sql":"SELECT `country` AS `country_name`, `gdp` AS `gdp_usd` FROM `Sample_Database`.`sample_country_gdp` WHERE `year` = '2025' AND `country` = '中国'","tables":["sample_country_gdp"],"chart-type":"table"}
+  example_answer_3_with_limit: |
+    {"success":true,"sql":"SELECT `country` AS `country_name`, `gdp` AS `gdp_usd` FROM `Sample_Database`.`sample_country_gdp` WHERE `year` = '2025' AND `country` = '中国' LIMIT 1000","tables":["sample_country_gdp"],"chart-type":"table"}