docs(webcam): portal/Flatpak IR gap is v4l2-only (#71)

Ship the recommended document-only path: WirePlumber hideIrSensor acts
on the v4l2 monitor only; libcamera / xdg-desktop-portal / Flatpak
camera pickers can still list the internal IR sensor.

- HARDWARE.md §7: dual-sensor subsection (scope, workaround, deferred)
- ROADMAP § Webcam: ✓ #71; (b)/(c) stay hardware-gated
- README option row + HARDWARE-QUEUE T14s check for (b)/(c)
- Close BACKLOG #71; no libcamera rules

Verified: V0 (docs only).

docs/HARDWARE.md

@@ -250,6 +250,36 @@ needs a maintainer + hardware-queue coverage.
 | Model quirks missing | Set better `hardwareProfile` (see §8) | System |
 | OpenRGB / printing / Steam | `nomarchy.services.*` | System |
 
+### Dual-sensor webcam / IR hide
+
+Many dual-sensor modules (e.g. ThinkPad T14s) expose colour + IR as two
+identically named “Integrated Camera” nodes. Picking the IR node yields a
+black/dark greyscale frame — the classic “my webcam is dark” symptom.
+
+`nomarchy.hardware.camera.hideIrSensor` (installer-on when RGB+IR names
+are detected; overridable `irMatch`) drops the IR node from **WirePlumber’s
+v4l2 monitor** so native PipeWire pickers only offer the colour camera.
+The kernel `/dev/video*` node stays open, so Howdy-style face unlock still
+works. Design history: [ROADMAP § Webcam](ROADMAP.md).
+
+**What it does not cover:** apps that list cameras via **libcamera** or
+the **xdg-desktop-portal** / **Flatpak** camera path still see both
+sensors — a Flatpak Zoom (or similar) user can still pick the black IR
+“camera”. That is intentional: a blanket libcamera disable would risk
+external USB cams that need the libcamera path, and surgical internal-only
+libcamera rules could not match early enough (only `device.api` binds
+before the WirePlumber monitor rule).
+
+**Workaround:** prefer the colour device in the picker (or any non-IR
+name). Apps that default to the first v4l2 colour source without a picker
+are fine.
+
+**Further engineering (needs T14s-class hardware):** (b) a WirePlumber
+*libcamera* monitor rule disabling GREY-only nodes; (c) a libcamera/udev
+quirk at the libcamera layer. Neither is implemented — the recommended
+path is document-only until those can be verified on real dual-sensor
+hardware (see `agent/HARDWARE-QUEUE.md` › T14s).
+
 Theme switches never touch drivers (Home Manager only).
 
 ## 8. Unsupported or unlisted machines
@@ -364,7 +394,7 @@ Full tables: [README § options](../README.md). Hardware-shaped surface:
 | `nomarchy.hardware.fingerprint.enable` / `.pam` | fprintd + PAM |
 | `nomarchy.hardware.npu.enable` | in-kernel NPU only |
 | `nomarchy.hardware.latestKernel` | `linuxPackages_latest` |
-| `nomarchy.hardware.camera.hideIrSensor` / `.irMatch` | dual-sensor webcams |
+| `nomarchy.hardware.camera.hideIrSensor` / `.irMatch` | dual-sensor webcams (v4l2 only; §7) |
 | `nomarchy.hardware.i2c.enable` / `.ddcci` | I2C + external backlight |
 | `nomarchy.system.power.*` | PPD/TLP, laptop, thermald, charge limit |
 | `nomarchy.system.bluetooth.enable` | BT stack |