FE+BE+DOCS: lock fields, devVlan not saveable

Signed-off-by: jokob-sk <jokob.sk@gmail.com>

docs/DEVICE_FIELD_LOCK.md

@@ -1,6 +1,8 @@
 # Quick Reference Guide - Device Field Lock/Unlock System
 
-## One-Minute Overview
+## Overview
+
+![Field source and locks](./img/DEVICE_MANAGEMENT/field_sources_and_locks.png)
 
 The device field lock/unlock system allows you to protect specific device fields from being automatically overwritten by scanning plugins. When you lock a field, NetAlertX remembers your choice and prevents plugins from changing that value until you unlock it.
 

docs/DEVICE_MANAGEMENT.md

@@ -49,6 +49,8 @@ To speed up device population you can also copy data from an existing device. Th
 
 ## Field Locking (Preventing Plugin Overwrites)
 
+![Field source and locks](./img/DEVICE_MANAGEMENT/field_sources_and_locks.png)
+
 NetAlertX allows you to "lock" specific device fields to prevent plugins from automatically overwriting your custom values. This is useful when you've manually corrected information that might be discovered differently by discovery plugins.
 
 ### Quick Start
@@ -64,7 +66,7 @@ The following 10 fields support locking:
 
 ### See Also
 
-- **For Users:** [Quick Reference - Device Field Lock/Unlock](QUICK_REFERENCE_FIELD_LOCK.md) - How to use field locking
+- **For Users:** [Quick Reference - Device Field Lock/Unlock](DEVICE_FIELD_LOCK.md) - How to use field locking
 - **For Developers:** [API Device Field Lock Documentation](API_DEVICE_FIELD_LOCK.md) - Technical API reference
 - **For Plugin Developers:** [Plugin Field Configuration (SET_ALWAYS/SET_EMPTY)](PLUGINS_DEV_CONFIG.md) - Configure which fields plugins can update