[BUG] opencodezen.toggleProvider disables provider

[tomludd]

🐛 What happened?

When calling OpenCode Zen: Remove/Re-add Provider in Language models, model is removed, but not added back in when called again.

🔄 Steps to reproduce

1. Run: OpenCode Zen: Remove/Re-add Provider in Language models
2. OpenCode Zen provider is gone.
3. OpenCode Zen: Remove/Re-add Provider in Language models
4. OpenCode Zen provider is still gone.

✅ What did you expect?

That OpenCode Zen Provider would be there.

🖥️ Environment

• Extension version: 0.7.5
• VS Code version: 1.137.0
• Provider: OpenCode Zen
• Model: non-free

📸 Workaround

Open user settings (json) and remove: "opencodezen.enabled": false

[ltmoerdani]

@tomludd Sorry about this one, and thanks for the workaround note, it actually pointed us straight at the bug.

Two things were wrong. The manage flow on agent variants wrote opencodezen-agent.enabled, a key nothing reads, while the provider gate only checks opencodezen.enabled, so the provider stayed removed no matter what the command did. And underneath that, the command was a blind on/off flip, so running it twice without a reload in between could never bring the provider back.

It's now a state-aware toggle: it shows you "Remove" or "Re-add" based on the current state, asks for confirmation, and the key it writes is always the real one. Retitled to "Toggle Provider Registration in Language Models" so it stops promising a behavior it didn't have. Fixed in #242, shipping in the next release. Deleting the stale key from settings.json is no longer needed.