docs(webcam): tuning tools in the app-suite template + libcamera gap filed

- templates/downstream/home.nix: commented "Webcam tuning" entries
  (cameractrls, v4l-utils) — bare packages, so template not toggle,
  per the option-surface rule; rarely needed since the IR-hide covers
  the common dual-sensor case.
- agent/BACKLOG.md PROPOSED: the portal/Flatpak camera picker still
  lists the internal IR sensor (libcamera path, untouched by the v4l2
  rule) — three options laid out, recommending document-only until a
  T14s-style machine is available to test a libcamera-side rule.

Closes BACKLOG NOW#7. Verified: V0 (flake check green; template still
evaluates through mkFlake).

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

agent/BACKLOG.md

@@ -42,13 +42,6 @@ exist, the story isn't written). Site-vs-markdown is a Decision (below).
 **Verify:** V0 + a mechanical option-surface diff (eval the options,
 compare to the tables — consider making that a permanent check).
 
-### 7. Webcam follow-ups (small)
-ROADMAP § Webcam: ship `v4l-utils` + `cameractrls` (commented app-suite
-entries or alongside the camera toggle — respect the option-surface
-rule) for genuine-tuning cases; write up the portal/Flatpak
-libcamera-path gap (internal IR still listed there) as a PROPOSED item
-with options. **Verify:** V1.
-
 ## NEXT
 
 ### 8. Complete-workstation viewers + default applications
@@ -187,7 +180,21 @@ earns ≥3 entries — keep the root at six.
 *Agents: append here with a one-paragraph pitch (what/why/cost). Do not
 implement. Bernardo moves accepted items into a tier.*
 
-- *(empty)*
+- **Portal/Flatpak camera picker still lists the internal IR sensor**
+  (ROADMAP § Webcam follow-up). The shipped IR-hide is a *WirePlumber
+  v4l2* rule, but Flatpak/portal apps consume cameras via the
+  **libcamera** path, where both sensors remain visible — a Flatpak
+  Zoom user can still pick the black IR "camera". Options, roughly
+  ascending cost: (a) do nothing — document it (portal camera support
+  is still rare in practice); (b) a WirePlumber *libcamera* monitor
+  rule disabling GREY-only nodes — needs verifying that libcamera
+  monitor rules can match early enough (the v4l2 investigation found
+  only `device.api` binds pre-rule, which is why surgical scoping
+  failed before — same wall likely applies); (c) a libcamera
+  configuration/udev quirk hiding the IR sensor at the libcamera layer
+  itself. Cost: (b)/(c) need a T14s-style RGB+IR machine to verify →
+  pairs with a hardware-queue session. Recommend (a) now, (b)
+  investigated when the T14s is next available.
 
 ## Decisions `[human]`