Update instructions to show nix run syntax

Users running via nix run don't have ./setup locally,
so show the full nix run command in output messages.
Uses generic placeholder for repo URL.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

setup

@@ -127,10 +127,10 @@ EOF
     echo "     cd $config_dir && git remote add origin <your-git-url> && git push -u origin main"
     echo ""
     echo "  2. On other devices, run:"
-    echo "     ./setup <git-url> <age-key>"
+    echo "     nix run 'git+<your-grapho-repo>' -- <config-git-url> <age-key>"
     echo ""
     echo "  3. To pair mobile:"
-    echo "     ./setup mobile"
+    echo "     nix run 'git+<your-grapho-repo>' -- mobile"
 }
 
 # =============================================================================
@@ -191,10 +191,10 @@ setup_join() {
         echo "This device: ${device_id:0:20}..."
         echo ""
         echo "Add this device on your other machines:"
-        echo -e "  ${BOLD}./setup add $device_id $(hostname)${NC}"
+        echo -e "  ${BOLD}nix run 'git+<your-grapho-repo>' -- add $device_id $(hostname)${NC}"
     fi
     echo ""
-    echo "To pair mobile: ./setup mobile"
+    echo "To pair mobile: nix run 'git+<your-grapho-repo>' -- mobile"
     echo "To sync:        ./scripts/usync"
 }
 
@@ -426,7 +426,7 @@ setup_mobile() {
         echo ""
         ok "Pairing complete! Devices should connect shortly."
     else
-        warn "No ID entered. Run './setup mobile' to try again."
+        warn "No ID entered. Run 'mobile' option again to retry."
     fi
 }