fix: add stylix compatibility shims for missing program options

Stylix unconditionally imports all target modules, which expect certain
program options to exist even when those programs aren't enabled. This
causes evaluation errors.

Add stylix-compat.nix with stub options for:
- programs.neovim.initLua (maps to extraLuaConfig)
- programs.opencode.tui/themes

Also:
- Disable neovim/neovide stylix targets (we deploy theme lua via theme-loader)
- Set autoEnable = false to only enable explicitly listed targets
- Enable programs.neovim to satisfy stylix's neovim target
- Update stylix to latest version

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

modules/home/stylix.nix

@@ -39,6 +39,7 @@ in
   stylix = {
     enable = lib.mkDefault true;
     enableReleaseChecks = lib.mkDefault false;
+    autoEnable = lib.mkDefault false;  # Disable auto-detection, explicitly enable targets
     image = lib.mkDefault activeWallpaper;
     base16Scheme = lib.mkDefault currentPalette;
 
@@ -80,6 +81,8 @@ in
     targets = lib.mkDefault {
       hyprland.enable = false; # We keep our custom hyprland config for borders/rules
       waybar.enable = false;   # We keep our custom waybar CSS
+      neovim.enable = false;   # We deploy theme lua files via theme-loader instead
+      neovide.enable = false;  # Neovide depends on neovim program module
       alacritty.enable = true;
       kitty.enable = true;
       gtk.enable = true;