feat: overhaul config — noctalia shell, niri keybinds, battery, extra packages

- niri: switch from replaceStrings patching to plain config.kdl for simplicity
- niri: add Mod+Shift+Q (close), Mod+Shift+HJKL/Arrow (move window),
  Mod+Shift+1-9 (move to workspace)
- niri: add layer-rule to disable background-blur on noctalia bar (fix seam)
- noctalia: add capsule_group for cpu+ram (group:sysmon), panel_overlap,
  contact_shadow; corner_radius_scale 1.0
- noctalia: add all LC_* locale overrides in plasma-localerc (fix vi_VN calendar)
- system: TLP (battery), UPower, disable power-profiles-daemon (conflicts with TLP)
- system: DDC/CI support (ddcutil + i2c-dev + hardware.i2c)
- system: enable fish shell system-wide
- packages: add tree, fish, ddcutil; noctalia required services documented
- README: full rewrite with current structure, keybinds, fresh-install steps

hosts/nixos/configuration.nix

@@ -74,6 +74,17 @@
   programs.firefox.enable = true;
   programs.niri.enable = true;
   programs.zsh.enable = true;
+  programs.fish.enable = true;
+
+  # Power management (TLP conflicts with power-profiles-daemon which Plasma enables
+  # by default, so explicitly disable it)
+  services.power-profiles-daemon.enable = false;
+  services.tlp.enable = true;
+  services.upower.enable = true;
+
+  # ddcutil: control external monitor brightness/contrast over DDC/CI
+  boot.kernelModules = [ "i2c-dev" ];
+  hardware.i2c.enable = true;
 
   security.polkit.enable = true;