island: headphones panel for Sony noise control

A headphones icon in the status pill, shown while Sony headphones are
connected, opens a panel in the capsule: battery, noise control tiles
(ANC, ambient, off), ambient level, focus on voice, the headphones' own
sink volume, power off and refresh.

Battery and volume need nothing new: BlueZ's Battery1 already reports the
charge, and volume is AVRCP through PipeWire, so the slider drives the
headphones' bluez_output node rather than the default sink. Only the mode
needs Sony's own protocol, which sonyctl speaks over RFCOMM with the
Python standard library. The headphones advertise the v2 MDR service on
channel 18 and answer an 8-byte init reply, which is the v2 shape.

What was measured on a WH-CH720N, and differs from what reading
Gadgetbridge alone suggested: the ambient subtype is 17, while 15 (what
Gadgetbridge sends to models without wind-noise reduction) is acked and
never answered; the set payload is 7 bytes, with no wind byte. Noise
cancelling has no strength, only on or off; a level sent with it is
ignored and the previous ambient level kept. Focus on voice reads back
as set. A connect right after the previous run closed fails with EBUSY,
so sonyctl retries it briefly.

Each call is about 2s, so the panel runs one at a time and sends the
ambient level only once the slider or wheel settles. The mode is re-read
on every open because the headphones' own button changes it too. Power
off was not exercised, to keep the headphones on during development.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

1 files changed, 16 insertions, 4 deletions

diff --git a/desktop/island/README.md b/desktop/island/README.md
index 9c33f41..9353f7e 100644
--- a/desktop/island/README.md
+++ b/desktop/island/README.md
@@ -47,10 +47,22 @@ is open or not. Click opens the calendar panel.
 
 ## Status pill
 
-Left to right: volume icon, tray, layout flag. The performance panel that
-used to open from here is the drawer's Performance page now
-(`desktop/modules/perf/`).
-
+Left to right: headphones icon, volume icon, tray, layout flag. The
+performance panel that used to open from here is the drawer's Performance
+page now (`desktop/modules/perf/`).
+
+- **Headphones icon** shows while Sony headphones are connected (a BlueZ
+  name starting `WH-`, `WF-` or `LinkBuds`). Click opens the headphones
+  panel: battery (BlueZ), noise control tiles (ANC, ambient, off), the
+  ambient level (1-20, drag or wheel, sent once it settles) and focus on
+  voice (both shown in ambient mode only), the headphones'
+  own sink volume (their `bluez_output` node, not the default sink; wheel
+  steps 5%, the icon mutes), power off and refresh. The mode goes
+  through `sonyctl`, which speaks Sony's v2 protocol over RFCOMM channel 18
+  and is read on every open, since the headphones' button changes it too.
+  Each call is about 2s, so the panel takes one at a time. Test:
+  `/usr/bin/python3 desktop/island/test_sonyctl.py` (codec only, no
+  Bluetooth).
 - **Volume icon** shows the default sink (muted, low, medium, high). Click
   opens the sound panel.
 - **Tray** shows `SystemTray` items. Left click activates, right click opens