docs(desktop): document Umbriel compositor configuration

docs/chezmoi/externals-and-ignore.mdx

@@ -130,8 +130,14 @@ mise tool versions stay local to each machine and are not managed.
 .config/niri/**
 .config/hypr
 .config/hypr/**
+.config/umbriel
+.config/umbriel/**
+.config/uwsm
+.config/uwsm/**
 .config/noctalia
 .config/noctalia/**
+.config/vicinae
+.config/vicinae/**
 .config/niri-dynamic-workspaces
 .config/niri-dynamic-workspaces/**
 .config/fontconfig
@@ -141,6 +147,7 @@ mise tool versions stay local to each machine and are not managed.
 .config/systemd/**
 .local/bin/kitty-day-save
 .local/bin/niri-launch
+.local/bin/umbriel-launch
 .config/fish/auto-Niri.fish
 .local/bin/cp-appid
 .local/bin/projects-sync
@@ -157,6 +164,14 @@ The block is emitted, and these paths skipped, unless the OS is `linux` and the
 
 See [Desktop](/desktop/niri) for what the layer contains. Gaps in the gate: the block lists `niri-launch` but not its siblings (`niri-launch-ai`, `niri-launch-browser`, `niri-launch-terminal`, `niri-launch-webapp`), and the waybar config (`dot_config/waybar/`) is not gated at all, so it applies on every role. `dot_config/niri/scripts/` is covered by `.config/niri/**`.
 
+### Generated theme files
+
+```txt
+.config/umbriel/noctalia.toml
+```
+
+Noctalia's umbriel template rewrites this file on every theme change, so it stays out of the repo on every machine. `config.toml` includes it as an optional file; see [Umbriel](/desktop/umbriel#theme).
+
 ### Secrets in runtime state
 
 ```txt