Port to Plasma 6 and switch to the local zerotier-one API

[Hafikan]

Zerotier Central's API needs an account token that is not available on the free plan, so the widget now talks to the local zerotier-one service on localhost:9993 instead. That trades the full membership roster of a network for what this machine actually sees: the networks it joined and the peers it is talking to, with latency and direct/relayed state.

A peer's address on the virtual network -- the one you connect to -- is not in the local API, since it is the controller that hands it out. It is recovered instead by deriving each peer's MAC from the network id and node id, then looking that up in the interface's neighbour table.

The port itself: metadata.json, PlasmoidItem, Kirigami units and theme, PlasmaExtras.Representation with a PlasmoidHeading, and KCM.SimpleKCM config pages. Emoji status markers became theme-coloured dots, the panel icon is now a symbolic SVG that follows the panel colour, and the separate network selector window is gone -- networks are picked inline in the settings.

Fixes carried over from the old Central code:

• Stale replies landing after a clear() duplicated the list; requests now carry a generation and late ones are dropped.
• With no token configured, a retry timer restarted itself every 5s forever. Reloads are driven by configuration changes instead.
• The online count summed the server's onlineMemberCount on every reply, so it grew without bound and disagreed with the list next to it.
• ConfigGeneral declared cfg_zerotierToken twice and used string literals as ids, and its network selector window was parented to an undefined id.
• Removing a network from the selection used a regex over the comma separated list and could leave stray commas behind.

Note for anyone debugging this: Qt 6 blocks local file reads over XMLHttpRequest unless QML_XHR_ALLOW_FILE_READ=1 is set, and it fails silently -- the request never completes and no error is raised. The auth token is read through the executable data engine because of it.

[Duoslow]

Port to plasma 6 and other things okay but for the zerotier api there is no change needed zerotier still gives us the "API Access Tokens"

i'm on free plan and can generate new token and still acces the api succesfully?
also i was designed this way because if we use "Zerotier Central's API" user can access the network/user list without the zerotier installed.
maybe we can create a branch for this version.