docs: add CLAUDE.md with repo architecture and development commands

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

CLAUDE.md

@@ -0,0 +1,92 @@
+# CLAUDE.md
+
+This file provides guidance to Claude Code (claude.ai/code) when working with code in this repository.
+
+## Commands
+
+```bash
+# Apply configuration (switch/boot/test)
+sudo nixos-rebuild switch --flake '.#jupiter'
+sudo nixos-rebuild switch --flake '.#mibook'
+
+# Build without switching (CI-style check)
+nix build '.#nixosConfigurations.jupiter.config.system.build.toplevel'
+
+# Update all flake inputs
+nix flake update
+
+# Format Nix files
+nixfmt-rfc-style <file>   # or: find . -name '*.nix' | xargs nixfmt-rfc-style
+```
+
+## Architecture
+
+This is a flake-parts NixOS configuration for two machines:
+
+- **jupiter** — home server running media/automation services
+- **mibook** — laptop running KDE desktop + development tools
+
+### Module Loading Chain
+
+```
+flake.nix
+└── machines/configuration.nix        # flake-parts module; defines nixosConfigurations
+    ├── machines/core/                 # base modules applied to every machine
+    │   ├── core.nix                   # system packages, locale, timezone
+    │   ├── network.nix
+    │   ├── nix.nix
+    │   └── users.nix
+    ├── modules/                       # custom NixOS option modules (my.profiles.*, my.hardware.*, my.services.*)
+    │   ├── environments/              # per-service/app profiles
+    │   ├── hardware/                  # hardware profiles (nvidia, bluetooth, sound, wifi)
+    │   └── services/                  # infrastructure services (vpn, webserver)
+    └── machines/<name>/
+        ├── configuration.nix          # machine-specific NixOS settings
+        ├── environments.nix           # enables profiles via my.profiles.* / my.hardware.* options
+        ├── disks.nix
+        └── hardware-configuration.nix
+```
+
+### Profile / Module Pattern
+
+Every module under `modules/` follows the same structure:
+
+```nix
+{ config, lib, pkgs, ... }:
+let cfg = config.my.profiles.<name>; in
+{
+  options.my.profiles.<name>.enable = lib.mkEnableOption "...";
+  config = lib.mkIf cfg.enable { ... };
+}
+```
+
+Namespaces in use:
+- `my.profiles.*` — application/service profiles
+- `my.hardware.*` — hardware profiles
+- `my.services.*` — infrastructure services
+
+Profiles are enabled per-machine in `machines/<name>/environments.nix`.
+
+### Unstable Packages
+
+`pkgs.unstable` is available everywhere via an overlay defined in `machines/configuration.nix`. Use it when a package isn't in the pinned stable channel (`nixpkgs/nixos-25.11`).
+
+### Homepage Dashboard Integration
+
+Modules that expose a web UI can self-register with the homepage dashboard by adding to `my.homepage.services`:
+
+```nix
+my.homepage.services = [{
+  group = "Services";
+  name = "My Service";
+  description = "...";
+  href = "http://${hostName}:PORT";
+  icon = "si-iconname";  # optional
+}];
+```
+
+### Adding a New Service Module
+
+1. Create `modules/environments/<name>/default.nix` following the profile pattern above.
+2. Add `./environments/<name>` to `modules/environments/default.nix` (or the relevant `default.nix`).
+3. Enable it in the target machine's `machines/<name>/environments.nix`.