refactor: make hosts declarative and consolidate shared config

- add my.username / my.gaming.enable / my.ai.local.enable options and
  gate optional app modules on them instead of per-host import lists
- move vendor-neutral hardware.graphics into modules/graphical, leaving
  only NVIDIA-specific drivers and env vars in modules/hardware/nvidia
- derive the primary user everywhere from my.username (users, getty,
  home-manager, tmpfiles)
- de-duplicate Hyprland autostart down to a single system loginShellInit
  using the start-hyprland wrapper
- consolidate all nixpkgs overlays into modules/core/nix.nix and use
  final.stdenv.hostPlatform.system
- make the zsh rebuild helper target $(hostname) instead of hardcoded hades
- add nixpkgs follows for nixos-hardware, pi and comfy-ui (single nixpkgs)
- add .gitignore and a nixfmt flake formatter; format all nix files
- remove empty browser.nix/display-configuration.nix and rename
  local_ai.nix -> local-ai.nix
- document the my.* toggles in the README

home/foot.nix

@@ -1,14 +1,22 @@
 { pkgs, inputs, ... }:
 
 let
-  herdrPkg = if (inputs ? herdr && inputs.herdr ? packages && inputs.herdr.packages ? ${pkgs.stdenv.hostPlatform.system})
-    then inputs.herdr.packages.${pkgs.stdenv.hostPlatform.system}.default
-    else (pkgs.herdr or null);
+  herdrPkg =
+    if
+      (
+        inputs ? herdr
+        && inputs.herdr ? packages
+        && inputs.herdr.packages ? ${pkgs.stdenv.hostPlatform.system}
+      )
+    then
+      inputs.herdr.packages.${pkgs.stdenv.hostPlatform.system}.default
+    else
+      (pkgs.herdr or null);
 
   herdrPicker = pkgs.writeShellScriptBin "herdr-picker" (builtins.readFile ./scripts/herdr-picker.sh);
 in
 {
-  home.packages = (if herdrPkg != null then [ herdrPkg ] else []) ++ [
+  home.packages = (if herdrPkg != null then [ herdrPkg ] else [ ]) ++ [
     herdrPicker
   ];
 
@@ -51,24 +59,24 @@ in
         # Cursor text and cursor (background) colors
         cursor = "0e0e0e cffc00";
 
-        regular0 = "0e0e0e";  # bgSecondary
-        regular1 = "ff7a59";  # accentCoral
-        regular2 = "cffc00";  # accentVolt (green)
-        regular3 = "e3ff66";  # accentVoltLight (yellow)
-        regular4 = "00bfff";  # accentBlue
-        regular5 = "c6c6c7";  # Neutral Gray (magenta)
-        regular6 = "66d9ff";  # Light Cyan
-        regular7 = "e5e2e1";  # textSecondary
+        regular0 = "0e0e0e"; # bgSecondary
+        regular1 = "ff7a59"; # accentCoral
+        regular2 = "cffc00"; # accentVolt (green)
+        regular3 = "e3ff66"; # accentVoltLight (yellow)
+        regular4 = "00bfff"; # accentBlue
+        regular5 = "c6c6c7"; # Neutral Gray (magenta)
+        regular6 = "66d9ff"; # Light Cyan
+        regular7 = "e5e2e1"; # textSecondary
 
         # Bright Colors
-        bright0 = "2a2929";   # surfaceVariant
-        bright1 = "ff9a82";   # Bright Coral
-        bright2 = "dfff66";   # Bright Lime
-        bright3 = "f0ff8c";   # Bright Volt
-        bright4 = "66d9ff";   # Bright Blue
-        bright5 = "e0e0e1";   # Bright Gray
-        bright6 = "99e6ff";   # Bright Cyan
-        bright7 = "ffffff";   # textPrimary
+        bright0 = "2a2929"; # surfaceVariant
+        bright1 = "ff9a82"; # Bright Coral
+        bright2 = "dfff66"; # Bright Lime
+        bright3 = "f0ff8c"; # Bright Volt
+        bright4 = "66d9ff"; # Bright Blue
+        bright5 = "e0e0e1"; # Bright Gray
+        bright6 = "99e6ff"; # Bright Cyan
+        bright7 = "ffffff"; # textPrimary
 
         # Selection & URLs - volt lime selection like the site
         selection-foreground = "0e0e0e";