dhi: add eu data residency

[craig-osterhout]

Description

Document EU data residency for Docker Hardened Images. Docker can provision a DHI subscription in the EU region. When it does, Docker stores the organization's mirrored and customized images in the EU.

Page	What changed
eu-region.md	New page. How the region is set and checked, what Docker stores in the EU, and the limitations: no file content in customizations, no VEX for customized images, and Docker Scout isn't turned on automatically
customize.md	Notes that file content and the paths field aren't supported in the EU region. Renames the Scripts section to Files to match the UI, and adds the Symlinks section
mirror.md	Adds a section about mirrors in the EU region, including that mirrors created before the move stay in their original region
platform.md	Q3 2026 release note for EU data residency
_index.md	Adds a grid card for the new page
dhi.md	Tip in the Usage section that points to EU data residency

Related issues or tickets

RG-4464, DSB-69, DSB-174

Reviews

• Technical review
• Editorial review
• Product review

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