docs: establish domain model, MVI spec, and 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/plasma-org.kde.plasma.desktop-appletsrc

@@ -0,0 +1,173 @@
+[ActionPlugins][0]
+MiddleButton;NoModifier=org.kde.paste
+RightButton;NoModifier=org.kde.contextmenu
+
+[ActionPlugins][1]
+RightButton;NoModifier=org.kde.contextmenu
+
+[Containments][23]
+activityId=
+formfactor=2
+immutability=1
+lastScreen=0
+location=4
+plugin=org.kde.panel
+wallpaperplugin=org.kde.image
+
+[Containments][23][Applets][24]
+immutability=1
+plugin=org.kde.plasma.kickoff
+
+[Containments][23][Applets][24][Configuration]
+popupHeight=593
+popupWidth=789
+
+[Containments][23][Applets][24][Configuration][ConfigDialog]
+DialogHeight=540
+DialogWidth=720
+
+[Containments][23][Applets][24][Configuration][General]
+favoritesPortedToKAstats=true
+icon=org.cachyos.hello
+systemFavorites=suspend\\,hibernate\\,reboot\\,shutdown
+
+[Containments][23][Applets][24][Configuration][Shortcuts]
+global=Alt+F1
+
+[Containments][23][Applets][25]
+immutability=1
+plugin=org.kde.plasma.pager
+
+[Containments][23][Applets][26]
+immutability=1
+plugin=org.kde.plasma.icontasks
+
+[Containments][23][Applets][26][Configuration][ConfigDialog]
+DialogHeight=630
+DialogWidth=810
+
+[Containments][23][Applets][26][Configuration][General]
+launchers=
+
+[Containments][23][Applets][27]
+immutability=1
+plugin=org.kde.plasma.marginsseparator
+
+[Containments][23][Applets][28]
+activityId=
+formfactor=2
+immutability=1
+lastScreen=0
+location=4
+plugin=org.kde.plasma.systemtray
+popupHeight=432
+popupWidth=432
+wallpaperplugin=org.kde.image
+
+[Containments][23][Applets][28][Applets][29]
+immutability=1
+plugin=org.kde.kdeconnect
+
+[Containments][23][Applets][28][Applets][30]
+immutability=1
+plugin=org.kde.kscreen
+
+[Containments][23][Applets][28][Applets][31]
+immutability=1
+plugin=org.kde.plasma.cameraindicator
+
+[Containments][23][Applets][28][Applets][32]
+immutability=1
+plugin=org.kde.plasma.clipboard
+
+[Containments][23][Applets][28][Applets][33]
+immutability=1
+plugin=org.kde.plasma.devicenotifier
+
+[Containments][23][Applets][28][Applets][34]
+immutability=1
+plugin=org.kde.plasma.keyboardlayout
+
+[Containments][23][Applets][28][Applets][35]
+immutability=1
+plugin=org.kde.plasma.manage-inputmethod
+
+[Containments][23][Applets][28][Applets][36]
+immutability=1
+plugin=org.kde.plasma.notifications
+
+[Containments][23][Applets][28][Applets][37]
+immutability=1
+plugin=org.kde.plasma.keyboardindicator
+
+[Containments][23][Applets][28][Applets][37][Configuration][General]
+migrated=true
+
+[Containments][23][Applets][28][Applets][38]
+immutability=1
+plugin=org.kde.plasma.weather
+
+[Containments][23][Applets][28][Applets][40]
+immutability=1
+plugin=org.kde.plasma.battery
+
+[Containments][23][Applets][28][Applets][41]
+immutability=1
+plugin=org.kde.plasma.brightness
+
+[Containments][23][Applets][28][Applets][42]
+immutability=1
+plugin=org.kde.plasma.networkmanagement
+
+[Containments][23][Applets][28][Applets][43]
+immutability=1
+plugin=org.kde.plasma.volume
+
+[Containments][23][Applets][28][Applets][43][Configuration][General]
+migrated=true
+
+[Containments][23][Applets][28][Applets][44]
+immutability=1
+plugin=org.kde.plasma.bluetooth
+
+[Containments][23][Applets][28][Applets][47]
+immutability=1
+plugin=org.kde.plasma.mediacontroller
+
+[Containments][23][Applets][28][General]
+extraItems=org.kde.kscreen,org.kde.plasma.battery,org.kde.plasma.brightness,org.kde.plasma.cameraindicator,org.kde.plasma.clipboard,org.kde.plasma.devicenotifier,org.kde.plasma.keyboardlayout,org.kde.plasma.manage-inputmethod,org.kde.plasma.mediacontroller,org.kde.plasma.networkmanagement,org.kde.plasma.notifications,org.kde.plasma.volume,org.kde.kdeconnect,org.kde.plasma.bluetooth,org.kde.plasma.keyboardindicator,org.kde.plasma.weather
+knownItems=org.kde.kscreen,org.kde.plasma.battery,org.kde.plasma.brightness,org.kde.plasma.cameraindicator,org.kde.plasma.clipboard,org.kde.plasma.devicenotifier,org.kde.plasma.keyboardlayout,org.kde.plasma.manage-inputmethod,org.kde.plasma.mediacontroller,org.kde.plasma.networkmanagement,org.kde.plasma.notifications,org.kde.plasma.volume,org.kde.kdeconnect,org.kde.plasma.bluetooth,org.kde.plasma.keyboardindicator,org.kde.plasma.weather
+
+[Containments][23][Applets][38]
+immutability=1
+plugin=org.kde.plasma.digitalclock
+
+[Containments][23][Applets][38][Configuration]
+popupHeight=400
+popupWidth=560
+
+[Containments][23][Applets][39]
+immutability=1
+plugin=org.kde.plasma.showdesktop
+
+[Containments][23][General]
+AppletOrder=24;25;26;27;28;38;39
+
+[Containments][4][Wallpaper][org.kde.image][General]
+Image=/usr/share/wallpapers/cachyos-wallpapers/north.png
+PreviewImage=/usr/share/wallpapers/cachyos-wallpapers/north.png
+SlidePaths=/usr/share/wallpapers/
+
+[Containments][43]
+ItemGeometries-1920x1080=
+ItemGeometriesHorizontal=
+activityId=4dfe7a63-75b1-4532-89bb-9e8ebc7e360d
+formfactor=0
+immutability=1
+lastScreen=0
+location=0
+plugin=org.kde.plasma.folder
+wallpaperplugin=org.kde.image
+
+[ScreenMapping]
+itemsOnDisabledScreens=