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

modules/graphical/default.nix

@@ -1,41 +1,58 @@
-{ pkgs, lib, ... }:
+{
+  config,
+  pkgs,
+  lib,
+  ...
+}:
 
 {
-    programs.hyprland = {
-        enable = true;
-        xwayland.enable = true;
-    };
+  programs.hyprland = {
+    enable = true;
+    xwayland.enable = true;
+  };
 
-    services.getty.autologinUser = "anish";
+  services.getty.autologinUser = config.my.username;
 
-    # Boot straight into Hyprland from the first virtual console on any machine.
-    # No display manager required; tty2-6 remain available as plain shells.
-    environment.loginShellInit = ''
-        if [ "$(tty)" = "/dev/tty1" ]; then
-            exec ${pkgs.hyprland}/bin/Hyprland
-        fi
-    '';
+  # Boot straight into Hyprland from the first virtual console on any machine.
+  # No display manager required; tty2-6 remain available as plain shells.
+  # The start-hyprland wrapper ships with programs.hyprland and sets up the
+  # session environment correctly.
+  environment.loginShellInit = ''
+    if [ "$(tty)" = "/dev/tty1" ]; then
+        exec start-hyprland
+    fi
+  '';
 
-    # Machine-agnostic Wayland session variables.
-    # GPU/vendor specific variables live with their hardware module (e.g. modules/hardware/nvidia.nix).
-    environment.sessionVariables = {
-        NIXOS_OZONE_WL = "1";
-        HYPRCURSOR_ENABLED = "1";
-        MOZ_ENABLE_WAYLAND = "1";
-        QT_QPA_PLATFORM = "wayland;xcb";
-        QT_WAYLAND_DISABLE_WINDOWDECORATION = "1";
-        CLUTTER_BACKEND = "wayland";
-        GDK_BACKEND = "wayland,x11,*";
-    };
+  # Vendor-neutral graphics stack. Vendor modules (e.g. modules/hardware/nvidia.nix)
+  # only add drivers and vendor-specific environment variables.
+  hardware.graphics = {
+    enable = true;
+    enable32Bit = true;
+  };
 
-    # Fonts used across the desktop shell (Silicon Volt theme):
-    # JetBrains Mono for terminal/UI mono, IBM Plex Sans for UI sans,
-    # Instrument Serif for display italics, Nanum Gothic Coding as mono fallback.
-    fonts.packages = with pkgs; [
-        nerd-fonts.jetbrains-mono
-        nerd-fonts.fira-code
-        font-awesome
-        ibm-plex
-        nanum-gothic-coding
-    ] ++ lib.optional (lib.hasAttr "instrument-serif" pkgs) pkgs.instrument-serif;
+  # Machine-agnostic Wayland session variables.
+  # GPU/vendor specific variables live with their hardware module (e.g. modules/hardware/nvidia.nix).
+  environment.sessionVariables = {
+    NIXOS_OZONE_WL = "1";
+    HYPRCURSOR_ENABLED = "1";
+    MOZ_ENABLE_WAYLAND = "1";
+    QT_QPA_PLATFORM = "wayland;xcb";
+    QT_WAYLAND_DISABLE_WINDOWDECORATION = "1";
+    CLUTTER_BACKEND = "wayland";
+    GDK_BACKEND = "wayland,x11,*";
+  };
+
+  # Fonts used across the desktop shell (Silicon Volt theme):
+  # JetBrains Mono for terminal/UI mono, IBM Plex Sans for UI sans,
+  # Instrument Serif for display italics, Nanum Gothic Coding as mono fallback.
+  fonts.packages =
+    with pkgs;
+    [
+      nerd-fonts.jetbrains-mono
+      nerd-fonts.fira-code
+      font-awesome
+      ibm-plex
+      nanum-gothic-coding
+    ]
+    ++ lib.optional (lib.hasAttr "instrument-serif" pkgs) pkgs.instrument-serif;
 }