feat(power): laptop power management (power-profiles-daemon + TLP)

Adds a `nomarchy.system.power.*` surface (modules/nixos/power.nix),
replacing the bare `services.upower` (Waybar reporting only) baseline:

- power-profiles-daemon ships by default; switched through polkit (no
  root prompt). TLP is the opt-in `backend = "tlp"` for deeper battery
  tuning — the two are mutually exclusive (asserted).
- thermald behind `power.thermal.enable` (Intel-only).
- `power.batteryChargeLimit` (e.g. 80): a backend-independent sysfs
  oneshot writes charge_control_end_threshold; gated on `power.laptop`.

Switcher + indicator live home-side and self-gate on a battery being
present + powerprofilesctl running, so they hide on desktops and under
TLP — no system->home wiring (like the Waybar battery widget):

- rofi.nix: `nomarchy-menu power-profile` module + a picker entry shown
  only on laptops with PPD.
- waybar.nix: first `custom/*` module — click cycles the profile.

Installer writes `power.laptop = true` (battery probe) and
`power.thermal.enable` (GenuineIntel) into the generated system.nix, and
scaffolds the charge limit commented-out.

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

README.md

@@ -412,23 +412,28 @@ close · `SUPER+1..9` workspaces · `Print` region screenshot.
   comments/docs for drift against the code; and re-check that every file
   still earns its place under the `modules`/`hosts`/`themes`/`pkgs`/`tools`
   rule of thumb.
-- **Laptop power / battery management:** today the distro does *no* active
-  power management — only `services.upower` is on, and that's just battery
-  *reporting* for the Waybar widget; CPU/thermal/charge behaviour is whatever
-  the kernel and the nixos-hardware profile default to. Add a real power
-  story behind a `nomarchy.system.power.*` surface, gated to laptops (the
-  installer already detects chassis):
-  - **profiles:** ship `power-profiles-daemon` by default (the upstream-
-    aligned choice — power-saver/balanced/performance via `powerprofilesctl`),
-    with a switcher in the rofi menu and a Waybar indicator. Offer **TLP** as
-    an opt-in for maximum battery life (note: mutually exclusive with PPD, and
-    more aggressive/opaque). **Decision to make:** PPD-default vs TLP-default.
-  - **thermal:** `thermald` on Intel (the Latitude is Intel) to avoid
-    throttling.
-  - **longevity:** battery charge thresholds (e.g. stop charging at ~80%)
-    where the hardware supports it.
-  - **cohere** with `modules/home/idle.nix` (idle lock / display-off /
-    suspend) and review logind lid handling so the power behaviours line up.
+- **Laptop power / battery management:** a real power story behind a
+  `nomarchy.system.power.*` surface (`modules/nixos/power.nix`), replacing the
+  old "only `services.upower` for Waybar reporting" baseline:
+  - ✓ **profiles:** `power-profiles-daemon` ships by default (the upstream-
+    aligned choice — power-saver/balanced/performance via `powerprofilesctl`,
+    switched through polkit so no root prompt). A `power-profile` menu module
+    (in the SUPER+M picker) and the first Waybar `custom/*` indicator (click to
+    cycle) both **self-gate** on a battery being present + PPD running, so they
+    hide on desktops and under TLP — no system→home wiring. **TLP** is the
+    opt-in (`backend = "tlp"`) for deeper battery tuning; the two are mutually
+    exclusive (asserted).
+  - ✓ **thermal:** `thermald` behind `power.thermal.enable`; the installer
+    turns it on for a `GenuineIntel` CPU.
+  - ✓ **longevity:** `power.batteryChargeLimit` (e.g. 80) — a backend-
+    independent sysfs oneshot writes `charge_control_end_threshold`. Off by
+    default; the installer scaffolds it commented-out on laptops.
+  - ✓ **installer:** writes `power.laptop = true` (battery probe) and
+    `power.thermal.enable` (Intel) into the generated `system.nix`.
+  - Remaining: **cohere** with `modules/home/idle.nix` (AC-vs-battery idle
+    timeouts / no auto-suspend on AC) and review logind lid handling, plus a
+    boot-only→event-driven charge-limit re-apply (udev) if a firmware resets
+    the threshold on unplug.
 - **Opt-in services & integrations:** the counterpart to the opt-*out*
   application suite above — heavier or more personal integrations shipped
   **off by default**, each a `nomarchy.services.<name>.enable` toggle a