fix anti-patterns: niri portals, nix optimise, zram; add dev packages

- niri: remove explicit package override (use niri-flake default), drop
  KDE portal, set xdg.portal.config for deterministic portal resolution,
  remove unused waybar
- core: replace synchronous auto-optimise-store with async
  nix.optimise.automatic, reduce zramSwap.memoryPercent from 300 to 100
- dev: add python3 and uv to system packages
- add .mcp.json (nixos MCP server) and CLAUDE.md

modules/niri.nix

@@ -7,16 +7,12 @@
 
     fonts.packages = [ pkgs.nerd-fonts.jetbrains-mono ];
 
-    programs.niri = {
-      enable  = true;
-      package = pkgs.niri;
-    };
+    programs.niri.enable = true;
 
     programs.gpu-screen-recorder.enable = true;
 
     environment.systemPackages = with pkgs; [
       quickshell-niri
-      waybar
       fuzzel
       swaylock
       swayidle
@@ -25,7 +21,6 @@
       slurp
       wl-clipboard
       xdg-desktop-portal-gnome
-      kdePackages.xdg-desktop-portal-kde
       xwayland-satellite
       gpu-screen-recorder-gtk
       libnotify
@@ -34,11 +29,9 @@
     ]; 
  
     xdg.portal = {
-      enable        = true;
-      extraPortals  = [
-        pkgs.xdg-desktop-portal-gnome 
-        pkgs.kdePackages.xdg-desktop-portal-kde
-      ];
+      enable       = true;
+      extraPortals = [ pkgs.xdg-desktop-portal-gnome ];
+      config.common.default = [ "gnome" ];
     };
 
     security.pam.services.swaylock = {};