Author winget manifest YAML for fallout-agent

[ChrisonSimtian]

Parent: #121

Author the three winget manifest YAML files for Fallout.Agent (Fallout.Agent.installer.yaml, Fallout.Agent.locale.en-US.yaml, Fallout.Agent.yaml) to the microsoft/winget-pkgs schema.

Definition of done

• Manifests stored in eng/winget/ (path TBD during implementation) inside this repo.
• winget validate --manifest eng/winget/ passes locally.
• Manifests rendered as templates with placeholders for version and installer URL so the release pipeline (W4) can substitute on tag.
• Schema version pinned to the current winget-pkgs manifestVersion.