Add web toggle for Bluetooth discoverable window

The board stays hidden by default, so new phones could only pair via an
SSH session. Add 'radxa-audio discoverable on|off' backed by a transient
radxa-bt-pairing unit that auto-approves and trusts devices pairing in
the window, expires on its own, and expose it in the web mixer with a
countdown.

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

scripts/input_controls.py

@@ -6,9 +6,11 @@ import re
 import subprocess
 import tempfile
 import os
+import time
 
 CONFIG = Path('/etc/radxa-audio/mixer.json')
 MEMORY = Path('/etc/radxa-audio/input-memory.json')
+PAIRING_UNTIL = Path('/run/radxa-audio/pairing-until')
 SPS = 'org.gnome.ShairportSync'
 SPS_PATH = '/org/gnome/ShairportSync'
 MAC = re.compile(r'(?:[0-9A-F]{2}:){5}[0-9A-F]{2}\Z')
@@ -148,6 +150,16 @@ def devices():
     return result
 
 
+def pairing():
+    adapter = next((i['org.bluez.Adapter1'] for i in objects('org.bluez', '/').values()
+                    if 'org.bluez.Adapter1' in i), {})
+    on = bool(adapter.get('Discoverable'))
+    remaining = 0
+    try: remaining = max(0, round(float(PAIRING_UNTIL.read_text()) - time.time()))
+    except (FileNotFoundError, ValueError): pass
+    return {'discoverable': on, 'remaining': remaining if on else 0, 'alias': adapter.get('Alias', '')}
+
+
 def dacs():
     result = []
     for line in command('aplay','-l').splitlines():
@@ -164,4 +176,6 @@ def state():
     except Exception as e: bluetooth=[]; issues.append(str(e))
     try: dac = dacs()
     except Exception as e: dac=[]; issues.append(str(e))
-    return {'config':config,'inputs':inputs(),'bluetooth':bluetooth,'dacs':dac,'issues':issues}
+    try: pair = pairing()
+    except Exception as e: pair={'discoverable':False,'remaining':0,'alias':''}; issues.append(str(e))
+    return {'config':config,'inputs':inputs(),'bluetooth':bluetooth,'dacs':dac,'pairing':pair,'issues':issues}