[Security] Add 2-day minimum release age cooldown (incident-51987)

[SeanMeyer]

Summary

• Adds npmMinimalAgeGate: "2d" to .yarnrc.yml to configure Yarn Berry to refuse packages published less than 2 days ago during lockfile generation
• Part of the security campaign (incident-51987) to add supply chain attack cooldowns across DataDog repositories
• Requires Yarn Berry >= 4.10.0 (this repo uses 4.12.0)

Test plan

• Verify yarn install still works with existing lockfile (no-op, existing packages are older than 2 days)
• Verify .yarnrc.yml is valid YAML and Yarn parses it correctly

🤖 Generated with Claude Code

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