Generate valid MCP local configuration for opencode

[mastermakrela]

This patch fixes issue #768, where sv add mcp generated an invalid configuration for the opencode client.
Previously, the addon produced a malformed config using "command": "npx" and a separate args field, which caused schema validation errors.

Fixes: #768

Changes

• Updated getLocalConfig to support both command and args as flexible inputs.
• Default command for local setup for opencode is now correctly defined as an array: ["npx", "-y", "@sveltejs/mcp"]; for other IDEs nothing has changed
• Made args optional, to avoid schema warning in OpenCode, i.e. when using array-style commands.

Notes

• I’ve looked at the contributing guidelines, and if I understand correctly, a changeset isn’t needed since this is part of an addon.
  If I'm wrong - I'll generate one :)
• I noticed there’s already an MCP test, but it doesn’t verify the generated output for specific IDEs. But if wanted, I can create one.

Result

The generated opencode.json now matches the official schema at
https://opencode.ai/config.json, preventing the “expected array, received string” error when running opencode.

Before	After

[changeset-bot]

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Latest commit: 20c9dd3

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[pkg-pr-new]

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commit: 20c9dd3

[manuel3108]

Looks correct according to their docs, thank you!
@jycouet Any idea if the docs were different when this addon was created, or which docs we were following?

[jycouet]

Thank you for doing this.
I added a test to save snapshots, it will be easier to see if things change.

Any idea if the docs were different when this addon was created, or which docs we were following

I looked at links again, I think it's just me that didn't read well! >< Too many at the same time ^^

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What do you think?