docs: refresh OneUptime vs Datadog comparison evidence

[simlarsen]

Summary

• refresh the canonical /compare/datadog source with first-party evidence validated on 2026-08-04
• distinguish Datadog's open-source Agent from its managed SaaS control plane
• add fair-fit language, prerequisites, limitations, and canonical source links
• remove illustrative savings and workload-cost claims that were not reproducible
• update public Datadog starting prices without treating modular plans as directly comparable

Claim/evidence standard

The page now cites OneUptime repository/docs/pricing and Datadog site, Agent, Workflow Automation, Agent source/license, and pricing pages. It explicitly states that this is not a benchmark or feature-parity claim and that self-hosting carries operational responsibility.

Checks

• git diff --check — passed
• TypeScript transpile of Home/Utils/ProductCompare.ts — passed
• cd Home && npm test -- --runInBand — could not run because dependencies are not installed in this checkout (jest: not found)

Publication

This PR is not published content. Do not announce the refreshed asset until it is merged and live.

[simlarsen]

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