Move Bulk OTA settings into OTA Updates; remove duplicate Restart button

[tashda]

Summary

Two small Settings cleanups:

1. Bulk OTA had its own Application-section row for two fields (Concurrency, Device Timeout) that govern how Shellbee paces "Check All for Updates". They're conceptually OTA settings — they belong with the rest of the OTA config the user already navigates into.
2. The bottom of Settings duplicated the Restart Zigbee2MQTT control that already exists on Settings → Server. One source of truth is enough.

Fix (commit on dev)

• OTASettingsView gains a "Bulk Check" section at the bottom with the Concurrency and Device Timeout fields (@AppStorage keys unchanged). AppPerformanceView deleted.
• SettingsView.applicationSection no longer surfaces a Bulk OTA navigation row.
• SettingsView.dangerSection no longer surfaces "Restart Zigbee2MQTT". The restart-required notice at the top of Settings still works (same alert), and ServerDetailView keeps its own Restart entry.

Acceptance criteria

• Settings → Integrations & Features → OTA Updates shows a "Bulk Check" section with the two fields.
• Settings → Application no longer lists Bulk OTA.
• Settings bottom no longer shows Restart; the restart-required banner at the top still triggers a restart.