Add and organize analytics reporting documentation

[pelcasandra]

Summary

• add English and Spanish guides for the Dashboard, Revenue, Performance, Demand Insights, Service Quality, Workload & Capacity, and data completeness reports
• organize the Analytics, Reporting & Attribution section into five navigation groups and connect related report guides
• clarify how report dates and later conversions are counted without exposing internal cohort terminology
• standardize eCommerce casing and refine Spanish analytics terminology across affected help content

Why

This brings the analytics help section in line with the product reporting model, makes the growing article collection easier to navigate, and gives customers clearer guidance for interpreting results and attribution.

Validation

• bundle exec jekyll build
• git diff --check
• verified the English and Spanish category pages and grouped article navigation on the local Jekyll server

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