feat: nb battery improvement

hosts/nb/configuration.nix

@@ -29,6 +29,7 @@ in {
       ./modules/mcp-global.nix
       ./modules/ollama.nix
       ./modules/qdrant.nix
+      ./modules/battery-brightness.nix
 
       ./cachix.nix
       ./users
@@ -74,7 +75,8 @@ in {
   users.defaultUserShell = pkgs.zsh;
 
   services.fwupd.enable = true;
-  services.irqbalance.enable = true;
+  # Disable irqbalance to save battery (not critical for laptop workloads)
+  services.irqbalance.enable = false;
 
   swapDevices = [ {
     device = "/nix/persist/swapfile";
@@ -87,6 +89,11 @@ in {
     "vm.dirty_ratio" = 10;
     "vm.dirty_background_ratio" = 5;
     "vm.vfs_cache_pressure" = 50;
+    # Battery optimization - increase dirty writeback time to batch writes
+    "vm.dirty_writeback_centisecs" = 3000;  # 30 seconds (default: 500 = 5s)
+    "vm.dirty_expire_centisecs" = 3000;     # 30 seconds (default: 3000)
+    # Enable laptop mode for aggressive disk power management
+    "vm.laptop_mode" = 5;
   };
 
   # nixos cross building qemu
@@ -112,7 +119,7 @@ in {
   };
 
   hardware.bluetooth.enable = true;
-  hardware.bluetooth.powerOnBoot = true;
+  hardware.bluetooth.powerOnBoot = false;  # Save battery - enable manually when needed
   hardware.bluetooth.settings = {
     General = { ControllerMode = "bredr"; };
   };