feat: add tailscale to mod-v2.json

[chicohaager]

Summary

Adds Tailscale as a community systemd-sysext module to the ZimaOS Mod-Store.

• Module repo: https://github.com/chicohaager/zimaos-tailscale-sysext
• Release asset: tailscale.raw (~36 MB, gzip-squashfs, Tailscale 1.96.4 amd64)
• License: BSD-3-Clause (Tailscale upstream); module scaffolding MIT.

What it ships

tailscaled runs as a native systemd service on the ZimaOS host — same model the upstream Buildroot recipe uses. State lives at /DATA/AppData/tailscale/ (so it survives ZimaOS updates). The module mirrors the chicohaager/cron precedent already in this list.

/usr/bin/{tailscale,tailscaled}
/usr/lib/systemd/system/tailscaled.service
/usr/lib/extension-release.d/extension-release.tailscale   # ID=_any

Why sysext and not Docker

Subnet-router and exit-node features need direct access to the host network stack (TUN, netfilter, policy routing). Running tailscaled inside a container on ZimaOS works for plain mesh, but loses the routing features and adds NAT hops. The sysext keeps the kernel fast-path and integrates with systemd-resolved.

Verification

Built and running on a ZimaCube Pro (ZimaOS v1.6.1, kernel 6.12.25, x86_64):

$ systemd-sysext list
HIERARCHY EXTENSIONS              SINCE
/usr      cron, tailscale, ...    ...

$ systemctl is-active tailscaled
active

$ tailscale status
... (logged in, IPv4 mesh up)

The squashfs is built with -comp gzip because the ZimaOS kernel does not enable CONFIG_SQUASHFS_ZSTD — using zstd here makes systemd-sysext refresh fail with Invalid argument.

One known limitation (kernel-side, not module-side)

Tailscale logs disabling tunneled IPv6 due to system IPv6 config: kernel doesn't support IPv6 policy routing. This is because the ZimaOS kernel ships without CONFIG_IPV6_MULTIPLE_TABLES / CONFIG_IPV6_SUBTREES. IPv4 tailnet is fully functional; only IPv6 tunneling is disabled. A separate kernel-config request can be filed against IceWhaleTech/ZimaOS if that's of interest — the sysext module itself can't fix this.

Test plan

• mod-v2.json is valid JSON (python3 -m json.tool)
• Entry follows the same repo-pattern as zima_cron and doconverter
• Release asset tailscale.raw exists at the linked URL and is publicly downloadable
• Module installs and runs on ZimaOS v1.6.1 (verified on hardware)