fix(core): preserve opencode provider settings

[joohw]

Summary

• Route OpenCode Claude and Gemini switches through the dedicated clovapi provider instead of mutating stock anthropic/gemini provider blocks.
• Limit OpenCode reset to removing clovapi-owned provider/model config so user-owned provider baseURL and apiKey values survive.
• Add regression coverage for pre-existing Anthropic and Gemini OpenCode settings across apply and reset, and bump the dev core version.

Test plan

• go test ./internal/apply
• go test ./...

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