Establish project foundation: domain model, MVI spec, environment reference

Capture the design work for the NixOS migration before any implementation:

- .claude/CONTEXT.md: domain glossary (Host, Module, Skeleton, Auto-loader,
  Enable convention, unstable/stable overlay)
- .claude/adr/0001-sops-nix-for-secrets.md: secrets tooling decision
- .claude/spec/laptop-mvi.md: frozen minimum-viable-install spec for neogaia

- reference/: read-only snapshot of the current CachyOS configs (secrets and
  state excluded), plus ENVIRONMENT.md profiling the live environment to guide
  replication

reference/home/.config/spectaclerc

@@ -0,0 +1,6 @@
+[ImageSave]
+lastImageSaveLocation=file:///home/alexion/Pictures/Screenshots/Screenshot_20260704_153951.png
+translatedScreenshotsFolder=Screenshots
+
+[VideoSave]
+translatedScreencastsFolder=Screencasts