Add Unreal Engine 5 skill family for Meta Quest / Horizon OS

[saurabhealtic]

Add Unreal Engine 5 skill family for Meta Quest / Horizon OS
What this adds

Four Agent Skills covering UE5 development for Meta Quest, filling the repo's current Unreal gap (existing skills are Unity / Spatial-SDK / WebXR; Unreal appears only as a passing option in hz-new-project-creation and hz-xr-simulator-setup):

hz-unreal-project-setup — Oculus-VR fork vs Epic UE5 + Meta XR plugin, fork tag matching, plugin enablement, Android/Vulkan packaging, mobile renderer settings, on-device launch via metavr.
hz-unreal-code-review — mobile-VR performance review: frame budget, Tick cost, Blueprint hotpaths, draw-call/overdraw, foveation/Multi-View.
hz-unreal-mr-passthrough — persistent passthrough (OculusXR Passthrough Subsystem), MR Utility Kit (MRUK) for scene understanding, Spatial Anchors, Depth API occlusion.
hz-unreal-interaction-sdk — Meta XR Interaction SDK, hand tracking feature status, microgestures.
Verification

Deprecation and version-gated claims were checked against live developers.meta.com docs; each skill carries a "Last verified" section with source URLs and doc Updated dates. Claims that could not be confirmed against an Unreal-specific page are explicitly flagged as open items rather than asserted (see below). hz-unreal-code-review is general engineering guidance rather than versioned doc claims, and is noted as such in-file.

For reviewers — items needing a maintainer's eye
Passthrough Layer Component deprecation: Meta's own docs give two conflicting anchors — the Persistent Passthrough page says "v74," the deprecated-node reference says "Unreal Engine 5.6." The skill discloses both rather than picking one.
arm64-only packaging: stated as standard practice but not found on an Unreal-specific doc page (only a general 64-bit Store policy). Flagged in-skill for confirmation.
Pose Detection v78+: the product-name qualifier is inferred from the page's numbering convention, not verbatim on that table row.
Notes

Skills follow house style: third-person descriptions naming Meta Quest and Horizon OS, under 500 lines each, metavr as the action layer. Each skill is a single self-contained SKILL.md. Happy to adjust structure or wording to match maintainer preference.

[meta-cla]

Hi @saurabhealtic!

Thank you for your pull request and welcome to our community.

Action Required

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Process

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[meta-cla]

Thank you for signing our Contributor License Agreement. We can now accept your code for this (and any) Meta Open Source project. Thanks!

[saurabhealtic]

Please let me know the next steps. When will it be merged?