Standardize file naming convention to use hyphens

Replace underscores with hyphens in file names to align with project
naming conventions. This improves consistency across the documentation.

Changes:
- Renamed pr_mr_summary.md to pr-mr-summary.md
- Renamed 11 image files from underscore to hyphen format
- Updated all references in markdown files and CSS

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <[email protected]>
Signed-off-by: even-wei <[email protected]>

Author: even-wei

docs/2-getting-started/get-started-jaffle-shop.md

@@ -75,16 +75,16 @@ Jaffle Shop is an example project officially provided by [dbt Labs](https://www.
    recce server
    ```
    Open the link http://0.0.0.0:8000, you can see the lineage diff
-   ![Lineage diff](../assets/images/2-getting-started/jaffle_shop_lineage.png)
+   ![Lineage diff](../assets/images/2-getting-started/jaffle-shop-lineage.png)
 8. Switch to the **Query** tab, run this query
    ```sql
    select * from {{ ref("orders") }} order by 1
    ```
    Click the `Run Diff` or press `Cmd + Shift + Enter`
    Click on the 🔑 icon next to the `order_id` column to compare records that are uniquely identified by their `order_id`.
-   ![Query in Recce](../assets/images/2-getting-started/jaffle_shop_query.png)
+   ![Query in Recce](../assets/images/2-getting-started/jaffle-shop-query.png)
 9.  Click the `+` to add the query result to checklist
-   ![Add query to checklist](../assets/images/2-getting-started/jaffle_shop_check.png)
+   ![Add query to checklist](../assets/images/2-getting-started/jaffle-shop-check.png)
 
 ## What’s Next
 By following this DuckDB tutorial, you’ve seen how Recce works locally.