Reach DDC on GPUs that are not "VGA", and stop warning about an empty dock

ddcutil's udev rule grants the seated user the GPU's i2c buses only when the
PCI class is 0x030000. An AMD iGPU that is not the primary boot display says
0x038000, so on the Framework every DDC bus stayed root-only. Ship the same
grant for the class the hardware actually reports; change-settings installs it.

And two conflations in the probe: an undocked laptop reported its normal state
as an error, and doctor collapsed every error into "No accessible DDC/CI bus".
Nothing external connected is now a clean empty -- doctor's unconfigured path
-- and a real failure surfaces the probe's own words, because an unreadable
bus and a monitor with DDC/CI off in its menu have different fixes.

Claude-Session: https://claude.ai/code/session_01Epx9ZC1gwm81K3jm9x9CKh

config/dot/quickshell/scripts/panama-brightness

@@ -93,7 +93,7 @@ bus_for_connector() {
 cmd_list() {
     has_accessible_bus || emit_error 'no I2C bus is accessible. ddcutil ships a udev rule that grants this, but only to devices created after it was installed. Run: sudo udevadm control --reload-rules && sudo udevadm trigger --subsystem-match=i2c-dev --subsystem-match=drm'
 
-    local rows=() connector bus value path
+    local rows=() externals=0 connector bus value path
     for path in "$DRM_ROOT"/card*-*; do
         [[ -e "$path/ddc" ]] || continue
         [[ "$(cat "$path/status" 2>/dev/null)" == "connected" ]] || continue
@@ -102,6 +102,14 @@ cmd_list() {
         connector="$(basename "$path")"
         connector="${connector#card*-}"
 
+        # Internal panels (eDP, LVDS, DSI) use the backlight, never DDC/CI.
+        # Counting only external connectors lets the empty result below say
+        # whether anything is even plugged in.
+        case "$connector" in
+            eDP-*|LVDS-*|DSI-*) ;;
+            *) externals=$((externals + 1)) ;;
+        esac
+
         bus="$(bus_for_connector "$path")"
         [[ "$bus" =~ ^[0-9]+$ ]] || continue
 
@@ -119,6 +127,13 @@ cmd_list() {
     done
 
     if [[ ${#rows[@]} -eq 0 ]]; then
+        # Nothing external is connected at all: the normal state of an
+        # undocked laptop, not a problem to warn about. The error path is
+        # reserved for a monitor that is present but will not talk.
+        if (( externals == 0 )); then
+            printf '{"displays":[],"error":""}\n'
+            return 0
+        fi
         emit_error 'no connected monitor reports DDC/CI brightness. Some panels implement it only when "DDC/CI" is enabled in their on-screen menu.'
     fi