feat(nix): zerotier overlay via clan inventory + mac ZT client 🕸️

Stage 4b of the clan migration. Declares a clan.inventory.instances.zerotier
instance with sunken-ship as controller and phantom-ship as peer (controller
is also listed as a peer so it joins its own network). Generates the network
ID, controller identity, and per-peer identities via `clan vars generate`;
all secrets are SOPS-encrypted to the user's age key and the per-machine
age keys.

- nixos/sops/ — clan-managed SOPS state (user + per-machine age keys).
- nixos/vars/ — shared + per-machine zerotier vars; *-identity-secret
  files are SOPS-encrypted, *.value files are plain public data.
- clan.core.networking.{targetHost,buildHost} = "danny@<host>" on both
  servers so `clan machines update` knows where to push and build.
- mac gets `zerotier-one` installed as a homebrew cask; authorization
  on the controller happens manually by node-ID in a follow-up step.

Known rough edges (to chase in later stages):
- zerotier-inventory-autoaccept.service races zerotierone.service on
  first activation (connection refused against the local API). Retrying
  the unit succeeds; clan upstream bug.
- Deployment must go through `clan machines update`, not plain
  nixos-rebuild, or the per-host SOPS age key isn't uploaded and
  zerotier-one can't decrypt its identity.

CLAUDE.md

@@ -67,6 +67,21 @@ Custom nix-darwin module at `nixos/ollama.nix` (upstream PR not yet merged). Ena
 
 Terminal colors follow **System Settings → Appearance**: `programs.alacritty` imports `~/.config/alacritty/active-colors.toml`; `scripts/alacritty-sync-system-theme.sh` copies Catppuccin latte/mocha there when the OS mode changes. **nix-darwin** `launchd.user.agents.alacritty-system-theme` polls every 30s; **fish** runs the same script on interactive startup. After changing Nix, one `darwin-rebuild switch`. Details: `assets/alacritty/README.md`.
 
+## clan.lol
+
+**CLI invocation:** clan-cli is not installed globally. Run ad-hoc via:
+
+```bash
+nix run git+https://git.clan.lol/clan/clan-core#clan-cli -- machines list \
+  --flake 'path:/Users/danny/dotfiles/nixos'
+```
+
+**Flake path quirk:** `--flake .` and `--flake git+…` both fail from a git worktree when the flake lives in a subdir (`nixos/`). Use `--flake 'path:…/nixos'` explicitly. May not be needed from the main checkout — retest.
+
+**`enableRecommendedDefaults = false`:** we opted out fleet-wide because clan's defaults flip to `systemd-networkd` + `systemd-resolved` + `boot.initrd.systemd`, which breaks dnsmasq (NAT DNS on phantom-ship) and navidrome's resolv.conf bind-mount on sunken-ship. Revisit per-service in a later pass — the defaults also include handy extras (tcpdump, htop, curl, jq, nixos-facter). Option defined in `nixosModules/clanCore/defaults.nix` + `nixosModules/clanCore/networking.nix` inside the `clan-core` flake.
+
+**Deployment:** `dotfiles-rebuild` timer (every 15 min pull) is still the source of truth. `clan machines update` works as a push escape hatch; dm-pull-deploy replaces the timer in a later stage.
+
 ## Shell
 
 Fish is the default shell. Bash auto-execs fish unless the parent process is already fish. Vi keybindings with fzf integration. Zoxide aliased to `cd`.