Fix BigQuery weekly active visitor history

[steve8708]

Summary

• Repair the known malformed weekly active visitor SQL on the canonical BigQuery dashboard.
• Add a regression test for non-empty SQL with an always-true time-range branch.

Verification

• Analytics repair spec: 21 passed
• Analytics typecheck passed
• pnpm guards: 71 passed
• Beta dashboard panel repaired and rendered with historical Jun-Sep data; corrected BigQuery query returned nonzero WAU values before Sep 1.

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Review Details

Incremental Code Review Summary

The latest increment adds an analytics changelog entry documenting the BigQuery active-user chart repair. The existing exact malformed-query repair and narrowly scoped QA smoke warning suppression remain unchanged from prior clean reviews. No actionable issue was identified in the available review results, and the changelog metadata/content is consistent with the analytics template changelog convention.

Risk assessment: Standard.

🧪 Browser testing: Skipped — no user-facing product UI changed; this increment adds changelog metadata only.