fix(hyprlua): only offer real capture nodes; show howdy's enroll error

The Brio (and most UVC webcams) expose a second /dev/video* node that is
metadata-capture only. The chooser listed it, the existence-only guard
accepted it, and howdy aborted with a bare exit 1 because that node can
never deliver a frame.

- list_cameras: skip nodes with no capture pixel formats (is_capture_device)
- howdy_camera_ok: require an actual capture node, not just an existing path,
  so a stale metadata-node device_path triggers reconfiguration
- howdy_add: tee howdy's output and surface the real reason on failure
  instead of only the exit code

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

desktopenvs/hyprlua/scripts/enroll-biometrics.sh

@@ -74,9 +74,18 @@ require_dialog() {
 }
 
 # ── Camera helpers ─────────────────────────────────────────────────────────────
+# True only for nodes that actually deliver video frames. UVC webcams expose
+# extra /dev/video* nodes for metadata capture (no pixel formats); pointing
+# howdy at one of those makes it fail to read a frame and abort with exit 1.
+is_capture_device() {
+    v4l2-ctl --device="$1" --list-formats 2>/dev/null \
+        | grep -qE '^[[:space:]]*\[[0-9]+\]:'
+}
+
 list_cameras() {
     for dev in /dev/video*; do
         [[ -c "$dev" ]] || continue
+        is_capture_device "$dev" || continue
         local id="${dev#/dev/video}"
         local name
         name=$(v4l2-ctl --device="$dev" --info 2>/dev/null \
@@ -277,10 +286,12 @@ howdy_set_cfg() {
 
 howdy_set_device_path() { howdy_set_cfg device_path "$1"; }
 
-# True when howdy points at a device node that actually exists.
+# True when howdy points at a node that exists AND can actually capture video
+# (not a metadata-only node, which would make enrollment fail with exit 1).
 howdy_camera_ok() {
     local dp; dp=$(howdy_get_device_path)
-    [[ -n "$dp" && "$dp" != none && -e "$dp" ]]
+    [[ -n "$dp" && "$dp" != none && -e "$dp" ]] || return 1
+    is_capture_device "$dp"
 }
 
 # howdy's stock tuning assumes a Windows-Hello IR sensor. A regular colour
@@ -356,7 +367,10 @@ howdy_add() {
     printf "\033[35m  ─────────────────────────────────────────\033[0m\n\n"
     printf "  Look at the camera and hold still.\n\n"
     # howdy has no label flag; the label is read from stdin during `add`.
-    printf '%s\n' "$name" | sudo howdy -U "$USER" add
+    # Tee the output so the actual reason (dark frames, no face, busy camera…)
+    # can be shown on failure instead of a bare exit code.
+    local log="$TMP_D/howdy_add.log"
+    printf '%s\n' "$name" | sudo howdy -U "$USER" add 2>&1 | tee "$log"
     local rc=${PIPESTATUS[1]}
 
     if [[ $rc -eq 0 ]]; then
@@ -364,7 +378,10 @@ howdy_add() {
             "Face model '$name' added.\n\nYou may need to relogin for PAM changes to take effect." \
             9 58
     else
-        msg "Failed" "Enrollment failed (code $rc).\n\nCheck camera and lighting." 8 52
+        local why; why=$(grep -vE '^\s*$' "$log" 2>/dev/null | tail -n 4)
+        msg "Failed" \
+            "Enrollment failed (code $rc).\n\nhowdy said:\n${why:-(no output captured)}\n\nIf it's a camera/frame error, re-run\n'configure camera' and pick another node." \
+            16 64
     fi
 }