fix: chart preview aggregation with pagination and sorting

[sentry]

This PR addresses issue DALGO-BACKEND-26C, where users encountered a ProgrammingError: UndefinedColumn when viewing chart data previews with pagination and sorting applied to aggregated metrics (e.g., COUNT(*)).

Root Cause:
The build_chart_query function in charts_service.py was structured such that when pagination was enabled, it would wrap the base table in a SELECT * subquery. However, the subsequent logic responsible for adding aggregation columns (like COUNT(*) AS "count_all_Total Count") and GROUP BY clauses was nested within the else block (the non-paginated path). This meant that for paginated queries, no aggregation columns were ever added to the main query.

When chart-level sorting was then applied, it would correctly translate the user-facing metric alias (e.g., "Total Count") into its internal SQL alias (e.g., "count_all_Total Count") and attempt to ORDER BY this column. Since the column did not exist in the SELECT clause of the paginated query, a ProgrammingError: UndefinedColumn occurred.

Solution:
To fix this, the chart-type-specific query building logic (which includes adding dimensions, metrics, and grouping) has been un-indented from the else block. This ensures that this core aggregation and column selection logic is applied universally, regardless of whether the initial data source is the raw table or a paginated subquery. As a result, when pagination is enabled, the aggregation columns will now be correctly added to the query, allowing sorting by these columns to succeed.

Fixes DALGO-BACKEND-26C

[sentry]

Codecov Report

❌ Patch coverage is 25.42373% with 44 lines in your changes missing coverage. Please review.
✅ Project coverage is 58.66%. Comparing base (75cb6fd) to head (94e7db1).

Files with missing lines	Patch %	Lines
ddpui/core/charts/charts_service.py	25.42%	44 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1385   +/-   ##
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  Coverage   58.66%   58.66%           
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  Files         132      132           
  Lines       15690    15690           
=======================================
  Hits         9205     9205           
  Misses       6485     6485           

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