Merge remote; add nix auto-GC and CLAUDE.md

Resolves conflict with upstream tmux/blender additions (already covered
by the per-program restructure). Adds weekly nix GC (--delete-older-than 7d),
store auto-optimise, and project CLAUDE.md.

CLAUDE.md

@@ -0,0 +1,46 @@
+# NixOS Dotfiles
+
+## Directory Layout
+
+```
+flake.nix                        # entry point, defines hosts
+hosts/
+  hivebrain/                     # marvin's main machine
+  nikita-nixos/                  # nikita's machine
+home/
+  packages-base.nix              # universal packages every host gets (neovim, ripgrep, etc.)
+  programs/                      # one file per installable program
+  fonts.nix                      # font config
+  rofi.nix                       # rofi config + packages
+  symlinks.nix                   # home-manager symlinks
+  tmux.nix                       # tmux config
+  yazi.nix                       # yazi config
+  zsh.nix                        # zsh config
+system/                          # NixOS system-level modules
+```
+
+## Adding a New Program
+
+1. Create `home/programs/<name>.nix`:
+
+```nix
+{ pkgs, ... }:
+{
+  home.packages = [ pkgs.<package-name> ];
+}
+```
+
+The filename is the program name; the package attribute can differ (e.g. `godot.nix` uses `pkgs.godot_4`).
+
+2. Add the import to whichever hosts should have it in `hosts/<host>/home.nix`:
+
+```nix
+../../home/programs/<name>.nix
+```
+
+## Rules
+
+- `home/packages-base.nix` — shared baseline, imported by every host. Only add truly universal tools here (shell utilities, editors).
+- `home/programs/` — one file per program. Hosts opt in by importing.
+- `home/<tool>.nix` (tmux, zsh, rofi, etc.) — for programs that need configuration beyond just installing a package. Same opt-in pattern via host imports.
+- `system/` modules are NixOS system-level config (not home-manager). Add them to `hosts/<host>/default.nix`.