[BUGFIX] fix cellSettings not applied for columns with no data in any query

[rajusem]

Summary

Fixes cellSettings conditional formatting (e.g., showing "N/A" for null values) not being applied for columns where no query returns any data — such as cpu_request_hard or memory_request_hard when no ResourceQuotas exist on the cluster.

Root cause

The keys array is computed only from data rows. When a query returns no data at all (empty series), its column key (e.g., value #5) never appears in any row and is therefore absent from keys. The keysAsObj extension then never adds undefined for that column, so the cellSettings null condition is never evaluated — resulting in blank cells instead of "N/A".

This is distinct from the filtering bug fixed in #688, where the column key existed in some rows but cellConfig indices were misaligned after filtering.

Fix

Include column names from columnSettings in the keys array, so that columns defined in the panel spec are always extended with undefined in keysAsObj and evaluated for cellSettings conditions — even when no query produces data for them.

How to reproduce (before fix)

1. Create a Table panel with multiple queries where one query returns no data at all (e.g., kube_resourcequota when no ResourceQuotas exist)
2. Define the empty query's column in columnSettings (e.g., value #5 as "CPU Request Hard")
3. Add cellSettings with a Misc/null condition (text: "N/A")
4. Other columns with partial data correctly show N/A
5. Bug: The column with no data shows blank instead of N/A

Tests added

• Column defined in columnSettings but with completely empty query data shows N/A for all rows
• Uses MOCK_MULTI_QUERY_DATA_EMPTY (empty series) to simulate the real-world scenario

Uses ARIA role-based selectors per UI guidelines.

Screenshots

Checklist

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