fix: move blocking subprocess calls off the async event loop

Wrap long-running synchronous calls in run_in_executor to prevent
the web UI from freezing during:

- wifi_scan (~20s scan)
- hotspot_enable / hotspot_disable (~60s each)
- bluetooth_scan (~12s scan)
- start_jack (~15s JACK restart) in set_audio_profile and save_settings

Each blocking call now runs in a thread executor, keeping the FastAPI
event loop responsive for other requests.

Added: functools.partial import, asyncio.get_event_loop() in two handlers.

src/web/server.py

@@ -21,6 +21,7 @@ import datetime
 from contextlib import asynccontextmanager
 from dataclasses import dataclass, field
 from pathlib import Path
+from functools import partial
 from typing import Any, Optional
 
 import uvicorn
@@ -1210,7 +1211,9 @@ class WebServer:
         async def wifi_scan():
             """Scan for available WiFi networks."""
             from ..system.network import wifi_scan
-            return {"networks": wifi_scan()}
+            loop = asyncio.get_event_loop()
+            networks = await loop.run_in_executor(None, wifi_scan)
+            return {"networks": networks}
 
         @app.get("/api/wifi/saved")
         async def wifi_saved():
@@ -1258,16 +1261,21 @@ class WebServer:
             Body: {ssid: str (optional), password: str (optional)}
             """
             from ..system.network import hotspot_enable
-            return hotspot_enable(
-                ssid=data.get("ssid", "Pi-Pedal"),
-                password=data.get("password", "pedal1234"),
+            loop = asyncio.get_event_loop()
+            result = await loop.run_in_executor(
+                None, partial(hotspot_enable,
+                    ssid=data.get("ssid", "Pi-Pedal"),
+                    password=data.get("password", "pedal1234"),
+                ),
             )
+            return result
 
         @app.post("/api/wifi/hotspot/disable")
         async def wifi_hotspot_disable():
             """Disable WiFi hotspot."""
             from ..system.network import hotspot_disable
-            return hotspot_disable()
+            loop = asyncio.get_event_loop()
+            return await loop.run_in_executor(None, hotspot_disable)
 
         # ── Bluetooth endpoints ──────────────────────────────────
 
@@ -1299,7 +1307,8 @@ class WebServer:
         async def bluetooth_scan():
             """Scan for discoverable Bluetooth devices."""
             from ..system.bluetooth import bt_scan
-            return bt_scan(timeout=12)
+            loop = asyncio.get_event_loop()
+            return await loop.run_in_executor(None, partial(bt_scan, timeout=12))
 
         @app.get("/api/bluetooth/paired")
         async def bluetooth_paired():
@@ -1426,6 +1435,7 @@ class WebServer:
             Changes are saved to ~/.pedal/config.yaml so they survive reboot.
             The switch restarts JACK (brief audio dropout ~1s).
             """
+            loop = asyncio.get_event_loop()
             audio_sys = self.deps.audio_system
             if not audio_sys:
                 raise HTTPException(status_code=503, detail="Audio system not available")
@@ -1519,13 +1529,13 @@ class WebServer:
             # exist until jack_client.start() recreates the JACK client below
             saved_auto_connect = audio_sys.config.auto_connect
             audio_sys.config.auto_connect = False
-            ok = audio_sys.start_jack(timeout=15)
+            ok = await loop.run_in_executor(None, partial(audio_sys.start_jack, timeout=15))
             audio_sys.config.auto_connect = saved_auto_connect
             if not ok:
                 # Rollback on failure
                 audio_sys.config.profile = old_key
                 logger.warning("JACK restart failed — attempting rollback to %s", old_key)
-                audio_sys.start_jack(timeout=15)
+                ok = await loop.run_in_executor(None, partial(audio_sys.start_jack, timeout=15))
                 if jack_client:
                     try:
                         jack_client.start()
@@ -1616,6 +1626,7 @@ class WebServer:
             Special handling:
               ``brightness`` — UI sends 1–10, stored as 0.1–1.0 float.
             """
+            loop = asyncio.get_event_loop()
             if self.deps.config is None:
                 raise HTTPException(status_code=503, detail="Config not available")
 
@@ -1670,7 +1681,7 @@ class WebServer:
                     audio_sys.stop_jack()
                     if jack_client:
                         jack_client.stop()
-                    ok = audio_sys.start_jack(timeout=10)
+                    ok = await loop.run_in_executor(None, partial(audio_sys.start_jack, timeout=10))
                     if not ok:
                         logger.warning("JACK restart failed after device change — rolling back")
                         # Restore old devices is complex, just log the failure