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/nvim/lua/keys.lua

@@ -0,0 +1,8 @@
+local map = vim.keymap.set
+
+map("n", "<C-h>", "<C-w>h", { desc = "Move focus left" })
+map("n", "<C-j>", "<C-w>j", { desc = "Move focus down" })
+map("n", "<C-k>", "<C-w>k", { desc = "Move focus up" })
+map("n", "<C-l>", "<C-w>l", { desc = "Move focus right" })
+
+map("n", "<Esc>", "<cmd>nohlsearch<CR>", { desc = "Clear search highlight" })