docs: factual-drift pass + i2c option docs (#47, #48)

Fix documentation drift (each claim verified against code): theme count
21→24; waybar whole-swap lists (waybar.css=5 incl. neon-glass vs
waybar.jsonc parity=4 + boreal); idle "suspend 30"→"15 min battery-only";
Tailscale sudo→operator; hosts/live.nix "No installer yet" header; link
docs/MIGRATION.md + fix its placeholder URL; README layout tree
(+doctor/control-center/battery-notify); OVERRIDES swappy→satty; document
always-on home pieces. String fixes: keybind cheatsheet
nmtui→networkmanager_dmenu; complete nomarchy-menu usage string
(+doctor/firmware/controlcenter/rollback). Add README rows for
nomarchy.hardware.i2c.* (#48) — closes checks.option-docs.

Implemented by a worktree agent; diff reviewed and cherry-picked.
Verified V0 (flake check) + checks.option-docs green + V1 (HM build).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

README.md

@@ -36,7 +36,7 @@ Flat on purpose. Two module trees, one options file each, no hidden layers.
 ├── flake.nix                      # inputs + the downstream API (exports below)
 ├── lib.nix                        # nomarchy.lib.mkFlake — one-call downstream wrapper
 ├── theme-state.json               # ★ THE single source of truth (git-tracked!)
-├── themes/                        # 21 presets: <slug>.json + optional <slug>/ assets
+├── themes/                        # 24 presets: <slug>.json + optional <slug>/ assets
 │   ├── nord.json                  #   palette (required, works alone)
 │   └── nord/                      #   assets (optional, fixed filenames)
 │       ├── backgrounds/           #     wallpapers (auto-picked, SUPER+SHIFT+T cycles)
@@ -62,6 +62,7 @@ Flat on purpose. Two module trees, one options file each, no hidden layers.
 │       ├── keybinds.nix           #   single source: Hyprland binds + SUPER+? sheet
 │       ├── swaync.nix             #   notifications, same JSON
 │       ├── idle.nix               #   hyprlock + hypridle, same JSON
+│       ├── battery-notify.nix     #   low-battery toasts at the bar's thresholds
 │       ├── yazi.nix               #   flagship TUI file manager + plugins
 │       ├── osd.nix                #   swayosd volume/brightness OSD
 │       ├── shell.nix              #   zsh + starship + bat/eza/zoxide
@@ -72,7 +73,10 @@ Flat on purpose. Two module trees, one options file each, no hidden layers.
 │   └── live.nix                   # bootable live ISO (try the distro, no install)
 ├── pkgs/
 │   ├── nomarchy-theme-sync/       # state writer + rebuild dispatcher (Python)
-│   └── nomarchy-install/          # live-ISO installer (gum + disko + mkFlake)
+│   ├── nomarchy-install/          # live-ISO installer (gum + disko + mkFlake)
+│   ├── nomarchy-doctor/           # read-only health sheet, one command per failure
+│   ├── nomarchy-control-center/   # TUI settings front-end over nomarchy-theme-sync (gum)
+│   └── nomarchy-battery-notify/   # low-battery toast watcher backing battery-notify.nix
 ├── templates/downstream/          # machine flake SoT (`flake init` + installer copy/patch)
 ├── docs/                          # human docs — map: docs/README.md
 │   ├── VISION.md                  #   product themes toward v1.0 (not a queue)
@@ -141,6 +145,10 @@ files), the two first rebuilds, and landing the checkout at
 `~/.nomarchy` so the theme CLI finds it. (The installer does all of
 this for you.)
 
+Already running NixOS on this machine? No reinstall needed — adopt
+Nomarchy in place, reusing your existing `hardware-configuration.nix`:
+**[docs/MIGRATION.md](docs/MIGRATION.md)**.
+
 You own two files day-to-day: `system.nix` and `home.nix` (plus
 `theme-state.json`, written by the CLI). Your `flake.nix` is set up once —
 later by the installer — and never hand-edited; it's a single call:
@@ -219,7 +227,7 @@ two tables below are split along exactly that line.
 | `nomarchy.rofi.enable` | `true` | Themed rofi launcher + `nomarchy-menu` dispatcher |
 | `nomarchy.swaync.enable` | `true` | swaync notifications, themed |
 | `nomarchy.batteryNotify.enable` | `true` | Low-battery toasts at the bar's thresholds — 25% low, 10% critical (stays up until dismissed); silent no-op on machines without a battery |
-| `nomarchy.idle.enable` | `true` | hyprlock + hypridle (idle lock 5 min, display off 10, suspend 30) |
+| `nomarchy.idle.enable` | `true` | hyprlock + hypridle (idle lock 5 min, display off 10, suspend 15 min — battery-only) |
 | `nomarchy.yazi.enable` | `true` | yazi TUI file manager, themed + curated plugins |
 | `nomarchy.osd.enable` | `true` | swayosd on-screen display for volume/brightness/mute |
 | `nomarchy.shell.enable` | `true` | zsh + starship prompt + bat/eza/zoxide (zsh is the default login shell) |
@@ -237,6 +245,14 @@ two tables below are split along exactly that line.
 | `nomarchy.themesDir` | Nomarchy's `themes/` | Where per-theme app overrides are probed |
 | `nomarchy.package` | overlay's `nomarchy-theme-sync` | The theme/state tool package, overridable if you fork it |
 
+**Always-on, no toggle by design:** `services.cliphist`, `services.udiskie`
+(automount + safe-removal toasts) and `services.easyeffects` (mic noise
+cancellation) ship unconditionally — small, low-risk pieces with no
+Nomarchy-specific config behind them (the toggle-vs-package rule in
+`agent/CONVENTIONS.md`). Disable one from `home.nix` with the plain HM
+option, e.g. `services.easyeffects.enable = lib.mkForce false;` — see
+**[docs/OVERRIDES.md](docs/OVERRIDES.md)**.
+
 **`system.nix`** (NixOS — the machine):
 
 | Option | Default | Purpose |
@@ -264,7 +280,9 @@ two tables below are split along exactly that line.
 | `nomarchy.hardware.npu.enable` | `false` | Opt-in/experimental: load the on-die NPU driver (`amdxdna`/`intel_vpu`); userspace runtime is BYO |
 | `nomarchy.hardware.latestKernel` | `false` | Opt-in: ship `linuxPackages_latest` instead of the default kernel — for very new hardware whose drivers landed recently |
 | `nomarchy.hardware.camera.hideIrSensor` | `false` | Hide a dual-sensor webcam's IR node from PipeWire so apps only ever see the colour camera (the "second, dark Integrated Camera"); installer-set on a paired RGB+IR webcam. `/dev/video*` stays open, so Howdy-style face unlock still works; `.irMatch` overrides the IR-name regex |
-| `nomarchy.services.tailscale.enable` | `false` | Opt-in: Tailscale mesh VPN (then `sudo tailscale up`) |
+| `nomarchy.hardware.i2c.enable` | `false` | I2C devices support — access to `/dev/i2c-*` (RGB controllers, sensors, DDC/CI monitor control) |
+| `nomarchy.hardware.i2c.ddcci` | `false` (distro default: **`true`**) | the ddcci-driver kernel module, exposing external monitors as standard backlight devices via DDC/CI so brightness keys and swayosd natively control them |
+| `nomarchy.services.tailscale.enable` | `false` | Opt-in: Tailscale mesh VPN — the login user is made the operator, so `tailscale up/down/set` and the System › VPN menu work without sudo |
 | `nomarchy.services.syncthing.enable` | `false` | Opt-in: Syncthing file sync as the login user (GUI at `127.0.0.1:8384`) |
 | `nomarchy.services.podman.enable` | `false` | Opt-in: rootless Podman (`docker` aliased to it) |
 | `nomarchy.services.flatpak.enable` | `false` | Opt-in: Flatpak + the Flathub remote |
@@ -365,15 +383,15 @@ per theme — a single place to look, unlike the old distro's split:
 | `waybar.jsonc` | whole-swap for the bar *layout* (must be plain JSON) |
 | `rofi.rasi` | **whole-swap**: replaces the generated launcher/menu theme entirely |
 
-Six ported themes ship a `waybar.css` identity (catppuccin, lumon, nord,
-retro-82, summer-day, summer-night). Custom user themes can live in
+Five themes ship a `waybar.css` identity (summer-day, summer-night,
+executive-slate, boreal, neon-glass). Custom user themes can live in
 `$NOMARCHY_PATH/themes/` (preset lookup) and `nomarchy.themesDir` (eval-time
 asset probe).
 
 ## 5. Day-to-day
 
 ```sh
-nomarchy-theme-sync list               # 21 presets (nord, gruvbox, rose-pine, …)
+nomarchy-theme-sync list               # 24 presets (nord, gruvbox, rose-pine, …)
 nomarchy-theme-sync apply kanagawa     # whole desktop, one generation (~a switch)
 nomarchy-theme-sync set ui.gapsOut 16  # tweak one knob (also a switch)
 nomarchy-theme-sync bg next            # cycle wallpapers — instant, no rebuild