DSH Opencode Zen Free Provider

Key features

• This plugin can access the free model of OpenCode Zen to dsh.
• The model only exposes the slots received upstream and does not create any slots.
• OpenCode Zen returns the non-certificate refusal (expired free amount, area limits, etc.) by HTTP 401/403, and dsshares classify these status codes as "API Key invalid".
• Plugin starts with the OpenCode Zen and Models.dev sync model directory with all metadata, only once, without rotation.
• Even if the pull failed at start-up, the plugin can be mounted properly and routed to an empty directory.