refactor(sql_explorer): Replace Plotly with SVG rendering for plots

Replaces the Plotly-based graph generation in the SQL Explorer with direct SVG rendering within an HTML template, similar to the exercise progress sparklines.

- Modifies `routes/sql_explorer.py` endpoints (`plot_query`, `plot_unsaved_query`) to fetch raw data instead of using pandas/Plotly.
- Adds `utils.prepare_svg_plot_data` to process raw SQL results, determine plot type (scatter, line, bar, table), normalize data, and prepare it for SVG.
- Creates `templates/partials/sql_explorer/svg_plot.html` to render the SVG plot with axes, ticks, labels, and basic tooltips.
- Removes the `generate_plot` function's usage for SQL Explorer and the direct dependency on Plotly for this feature.

templates/base.html

@@ -20,7 +20,6 @@
     <script src="/static/js/sweetalert2@11.js" defer></script>
     <!-- Mermaid -->
     <script src="/static/js/mermaid.min.js"></script>
-    <script src="/static/js/plotly-2.35.2.min.js" defer></script>
     <script>
         // Initialize Mermaid with startOnLoad set to false
         mermaid.initialize({