Standard fenrir backgrounding and -d flags restored.

docs/user.txt

@@ -15,15 +15,26 @@ Run these commands from the checkout root after building fenrir:
     # Linux text console, with console and keyboard device access
     sudo ./fenrir
 
+    # Linux console in the foreground (also use -f with service managers)
+    sudo ./fenrir -f
+
     # X11 terminal, as your regular user
     ./fenrir -x
 
     # Either mode can select the laptop layout
     ./fenrir -x --keyboard-layout laptop
 
-Fenrir runs in the foreground. Press Fenrir+Q to quit. Run only one
-reader on a given Linux console. Separate X11 terminal instances can run
-at once.
+Console mode starts in the background by default. Add -f to keep it in
+the foreground, including under a service manager. The launcher returns
+after the reader initializes and reports startup failures in the
+launching terminal. Use --debug-file PATH to retain diagnostics after
+detaching. Help, version, and configuration-only commands always run in
+the foreground.
+
+X11 mode (-x) always stays in the foreground because it owns the
+terminal and its child shell. Press Fenrir+Q to quit either mode. Run
+only one reader on a given Linux console. Separate X11 terminal
+instances can run at once.
 
 X11 mode starts a shell in a new PTY. The launching terminal must supply
 valid DISPLAY and WINDOWID environment variables. Keyboard interception
@@ -357,6 +368,9 @@ Fenrir runs as fenrir [options]. Use --help for the built-in reference.
 
   --version                            Print version and release channel
 
+  -f                                   Keep console mode in the foreground
+                                       (always enabled with -x)
+
   -x                                   Start a shell inside this X11
                                        terminal