Sources sidebar should be resizable, with width saved to config

[Yeraze]

Description

The Sources sidebar has a fixed width. On smaller screen resolutions or when source names are long, text is truncated and cannot be fully read. There is no way to widen the sidebar to see the full content.

Steps to Reproduce

1. Open MeshMonitor on a lower-resolution display or in a narrower browser window
2. Observe the Sources sidebar — source names, VN numbers, and status text may be cut off
3. There is no drag handle or resize option to widen the panel

Expected Behavior

• The Sources sidebar should be user-resizable via a drag handle on its edge
• The chosen width should persist across sessions, saved to a user/app config file (e.g. localStorage, user preferences, or a config JSON)
• Should respect minimum and maximum width bounds to prevent layout breakage

Additional Context

This is particularly impactful for MQTT broker sources whose names and topic paths tend to be longer than serial/BLE sources.

Authored by NodeZero 0️⃣

[BeerMan81]

the resizing could possiblly be tied to the suggested edit button here: #3355, this way the side bar can only be resized during edit mode...