Both the system option (`core/system/options.nix:theme`) and the home-side
state evaluator (`core/home/state.nix`) defaulted to "summer-night". The
installer-written state.json now seeds "nord" (see preceding installer
commit), and `lib/state-schema.nix` already defaults to "nord". Align the
hardcoded fallbacks here so a missing or blank state file lands on the
same theme everywhere instead of a now-inconsistent split.
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
6b2c678669