fix: complete hybridGPU wiring + make state-derived options overridable

Two related fixes that together close the "minimal wiring" gap behind
`nomarchy.system.features.hybridGPU`.

1. Complete the NVIDIA driver stack inside hardware.nix's hybridGPU
   mkIf block.

   Before: `hybridGPU = true` enabled supergfxd and... that was it.
   supergfxd manages mode switching by black/unblacklisting the nvidia
   kernel module, but without the rest of the NVIDIA stack actually
   loaded the dGPU has no driver to drive. Hyprland/Wayland silently
   stayed on the iGPU regardless of mode.

   After: hybridGPU=true also wires
     services.xserver.videoDrivers = ["nvidia"]   (loads the driver
                                                   under Wayland too)
     hardware.graphics.{enable,enable32Bit}
     hardware.nvidia.modesetting.enable           (required for
                                                   Wayland)
     hardware.nvidia.powerManagement.enable
     hardware.nvidia.package = config.boot.kernelPackages
                                      .nvidiaPackages.stable
     boot.kernelParams += "nvidia-drm.modeset=1"

   All wired with lib.mkDefault so a downstream system.nix can pin a
   beta driver, flip to the open kernel module, or set
   `hardware.nvidia.prime.{offload.enable, intelBusId, nvidiaBusId}`
   for render-offload. The bus IDs are per-machine (find via
   `lspci -D`) so they stay user-supplied; docs/OPTIONS.md has the
   full recipe.

2. Add lib.mkDefault to every state.json-derived assignment in
   core/system/state.nix and core/home/state.nix.

   Same priority bug on both sides: assignments like
   `features.hybridGPU = systemState.features.hybridGPU or false`
   landed at default priority. A downstream system.nix saying
   `nomarchy.system.features.hybridGPU = true` would then conflict
   with the state-derived value at the same priority, and Nix would
   refuse the merge with "conflicting definition values" — the
   user's override couldn't take effect.

   Verified by an explicit eval: extending the default nixosConfig
   with `nomarchy.system.features.hybridGPU = true` now resolves
   cleanly and the full driver stack engages.

   Side-effect: core/system/state.nix now reads from
   lib/state-schema.nix like the home side does, completing the
   schema-centralization started two batches ago.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

docs/ROADMAP.md

@@ -89,7 +89,7 @@ Each PR description should reference the row(s) in `docs/SCRIPTS.md` it closes,
 - Gaming preset (Next).
 - Vendor matchers in `installer/hardware-db.sh`: Steam Deck, Surface, ROG Ally, Snapdragon X laptops.
 - Surface support behind `nomarchy.hardware.isSurface` (Later).
-- Auto-detect dGPU presence and offer `programs.envycontrol`-style switching for the hybrid case (already gated behind `nomarchy.system.features.hybridGPU`, but the wiring is minimal).
+- Auto-detect dGPU presence in `installer/hardware-db.sh` and pre-fill `hardware.nvidia.prime.{intel,nvidia}BusId` in the generated `system.nix` (driver stack itself is Shipped — see entry below).
 
 ## 6. Pillar: Onboarding & docs
 
@@ -121,6 +121,7 @@ Each PR description should reference the row(s) in `docs/SCRIPTS.md` it closes,
 
 (Move items here when they land — keep them brief, link the commit/PR.)
 
+- _2026-05-18_ — Complete the hybrid-GPU wiring + fix unoverridable state-derived options. Two related fixes shipped together. **(1)** `nomarchy.system.features.hybridGPU = true` now wires the full NVIDIA driver stack (`services.xserver.videoDrivers = ["nvidia"]`, `hardware.graphics.{enable,enable32Bit}`, `hardware.nvidia.{modesetting,powerManagement}.enable`, `package = nvidiaPackages.stable`, `boot.kernelParams += "nvidia-drm.modeset=1"`) — was previously enabling only `supergfxd` mode-switching while leaving the system with no NVIDIA driver loaded, so mode switches silently no-op'd. All knobs use `lib.mkDefault` so a downstream `system.nix` can pin a beta driver, flip to the open kernel module, etc. Bus-ID prime config (per-machine) stays user-supplied — `docs/OPTIONS.md` has the full recipe. **(2)** Both `core/system/state.nix` and `core/home/state.nix` now use `lib.mkDefault` on every state.json-derived assignment, fixing a class of "I set X in my system.nix but it doesn't take effect" bugs (the state-derived value was at default priority and conflicted with the user's same-priority override). Side-effect cleanup: `core/system/state.nix` now also reads from `lib/state-schema.nix` like `core/home/state.nix` does, completing the schema-centralization started two batches ago. Verified `nix flake check` + an override test that flips hybridGPU via an overlay and confirms the entire driver stack engages.
 - _2026-05-18_ — Pillar 4: pre-flight resume polish. Fixed four resume-flow gaps in `installer/install.sh`: (1) `--resume` with a missing state file now errors loudly with a tmpfs explanation instead of silently falling through to a fresh prompt cycle (the most common operator confusion was "rebooted, forgot tmpfs eats /tmp/, watched the installer start over without realising"); (2) on resume, the saved target drive is validated as a block device before any disk-phase step runs — catches the live-ISO USB-unplugged / non-deterministic /dev/sdX class of mid-install failures; (3) `save_state` now stamps an ISO-8601 timestamp and `load_state` shows a `(saved Xm ago)` banner plus a `Target: /dev/X → user @ host` summary line, so the user can `Ctrl-C` if they're resuming onto the wrong host before any destructive prompt fires; (4) `--help` now documents the tmpfs limitation. `shellcheck --severity=error` passes.
 - _2026-05-18_ — Declarative-state defaults centralization. Made `lib/state-schema.nix` the single source of truth for every state-default that previously lived in three places (the schema itself, `core/system/options.nix` / `core/home/options.nix` `default = …` clauses, and `core/home/state.nix` `or …` fallbacks). Replaced ~25 hardcoded literals with `schema.<scope>.<key>` reads. Side-effect: fixed a lingering bug where `core/home/options.nix:theme` still defaulted to `"summer-night"` after the system-side was moved to `"nord"` — half the codebase's home option resolved to the wrong theme when state.json was missing/blank. `nix flake check --no-build` confirms zero semantic change for every other field. Doesn't touch the installer-written `state.json` (separate batch — needs schema → JSON generation).
 - _2026-05-18_ — Pillar 7 first step: Forgejo Actions CI (eval + lint). New `.forgejo/workflows/check.yml` runs on every push to `main` and every PR: (1) `nix flake check --no-build` to catch eval regressions, (2) `bash -n` + `shellcheck --severity=error` over every `nomarchy-*` bash script (whole-tree, not just changed files — gates branches that bypass the pre-commit hook), (3) `docs/SCRIPTS.md` drift check (fails loudly if a script change didn't regenerate the audit doc). All three checks pass locally on the current tree. Activation requires enabling Actions on the Forgejo repo and registering a `forgejo-runner`; the workflow itself is dormant until then. ISO build job is intentionally deferred — needs a binary cache (Cachix/Attic) to be tractable.