Fix duplicate experiment row after first experiment creation

[zackcl]

Resolves #3172

After creating the first experiment and navigating back to the Experiments page, the same experiment could appear twice until refresh.

This happened because the store treated totalExperiments = 0 as if the total count was unknown. When the detail page loaded the newly created experiment, the reducer changed totalExperiments from 0 to 1, which allowed the root page pagination logic to fetch and append the first page again.

This change preserves 0 as a valid loaded total count and only falls back to 1 when the total count is actually unknown (null or undefined). That keeps direct detail loading behavior intact while preventing the extra pagination fetch that caused the duplicate row.

[Copilot]

Pull request overview

Note

Copilot was unable to run its full agentic suite in this review.

Adjusts how totalExperiments is derived during single-experiment load/upsert actions to better distinguish “unknown total” from “confirmed empty list”, and updates the inline reducer comment accordingly.

Changes:

• Updates reducer logic to use nullish-coalescing for totalExperiments instead of a truthy check.
• Clarifies the intent in comments, including preserving 0 as a meaningful value.

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