Kea DHCP GUI: add option to flush active DHCP leases (parity with ISC DHCP)

[Tomipapa]

Description

• When using Kea DHCP in OPNsense, there is currently no GUI option to flush / clear active DHCP leases.
• In operational scenarios (e.g. network renumbering, VLAN changes, MAC reuse, test environments), being able to clear active leases is essential.
• At the moment, this requires dropping to the CLI and interacting directly with Kea’s control socket or lease database, which is inconvenient and inconsistent with the GUI-first workflow of OPNsense.
• Notably, this functionality already exists in the GUI when using ISC DHCP, which makes the limitation more visible when migrating to Kea.

Observed behaviour

1. Kea DHCP enabled
2. Active leases visible in GUI
3. No GUI control to:

• flush all leases
• flush leases per subnet
• flush a single lease

4. Operator must use CLI (kea-shell, lease DB manipulation, or service restart)

Expected behaviour

Provide a GUI action similar to ISC DHCP, for example:

• “Flush all leases” (global)
• “Flush leases for this subnet”
• (optional) “Release selected lease”

The action should:

• call Kea’s supported control interface (e.g. lease4-del, lease6-del, or database cleanup)
• be explicit and guarded (confirmation dialog)
• be logged for audit purposes

Why this matters

• Common operational requirement (testing, troubleshooting, renumbering)
• CLI access is not always desirable or available
• Breaks parity with existing ISC DHCP GUI
• Slows down routine operations
• Increases risk of human error when manipulating leases manually

Environment

• OPNsense 25.7.9 with Kea DHCP plugin
• Feature comparison point: ISC DHCP GUI lease management

Additional notes

• This request is about GUI parity and operator usability, not a Kea limitation.
• Kea already provides mechanisms to manage leases programmatically; exposing them in the GUI would significantly improve day-to-day operations.

Happy to help test or provide feedback on UX/behaviour if needed.