feat: add per-device custom Chrome production URL override

- Device model: add custom_chrome_url nullable column
- API: GET /api/wmt/config/<mac> returns device custom_chrome_url when set,
  falls back to WMTGlobalConfig.chrome_url for all other devices
- Web: device_edit POST saves/clears custom_chrome_url from form
- Template: wmt/device_form.html adds Chrome URL override section with
  clear status indicator (using global vs custom URL)
- DB: ALTER TABLE devices ADD COLUMN custom_chrome_url VARCHAR(500) applied

app/api/wmt.py

@@ -98,8 +98,8 @@ def get_device_config(mac_address):
             _, device_ts, latest_ts = _latest_config_ts(session, mac)
 
             payload = {
-                # Global settings
-                'chrome_url': global_cfg.chrome_url,
+                # Global settings (device custom_chrome_url overrides global chrome_url if set)
+                'chrome_url': (device.custom_chrome_url if device and device.custom_chrome_url else global_cfg.chrome_url),
                 'chrome_local_url': global_cfg.chrome_local_url or '',
                 'chrome_insecure_origin': global_cfg.chrome_insecure_origin,
                 'card_api_base_url': global_cfg.card_api_base_url,

app/models/__init__.py

@@ -52,6 +52,7 @@ class Device(Base):
     config_synced_at = Column(DateTime)        # set by server when client confirms in-sync
     info_reviewed_at = Column(DateTime, default=lambda: datetime(1970, 1, 1))
     card_presence = Column(String(10), default='enable')
+    custom_chrome_url = Column(String(500), nullable=True)  # per-device production URL override (overrides WMTGlobalConfig.chrome_url)
 
     # Relationships
     logs = relationship("LogEntry", back_populates="device")

app/web/wmt.py

@@ -299,6 +299,8 @@ def device_edit(device_id):
                 device.location = request.form.get('location', '').strip() or None
                 device.card_presence = request.form.get('card_presence', 'enable')
                 device.description = request.form.get('notes', '').strip() or None
+                custom_url = request.form.get('custom_chrome_url', '').strip()
+                device.custom_chrome_url = custom_url if custom_url else None
                 device.config_updated_at = datetime.utcnow()
                 device.info_reviewed_at = datetime.utcnow()
                 flash('Device updated.', 'success')