fix(opencode settings): support opencode zen and go endpoints switching

[ShiboSheng]

Summary

Fixes #260

Add explicit OpenCode Zen/Go endpoint support for key setup, auto-detection, and saved account editing.

Root Cause

OpenCode was treated as a single provider with a Go-biased default endpoint. The key validation path defaulted to OpenCode Go before Zen, and Settings did not expose a clear way to choose or switch between OpenCode Zen and OpenCode Go.

That caused Zen subscribers to see the wrong model catalog, and made endpoint switching require re-adding credentials.

Fix

• Default OpenCode validation/provider configuration to Zen instead of Go.
• Add explicit OpenCode Zen / OpenCode Go endpoint selection in the KeyVault setup flow.
• Preserve Go as a selectable endpoint and validate the chosen endpoint directly instead of silently falling back.
• Update OpenCode auto-detection so:
  • opencode keys can be checked against Zen or Go.
  • opencode-go keys are treated as Go-only.
  • detected candidates show their OpenCode endpoint in the selection modal.
• Allow existing OpenCode accounts to switch Zen/Go from the inline Edit tab without re-entering the API key.
• Refresh endpoint-specific model lists and persist the selected endpoint as the account base_url.
• Ensure Rust-native SDE provider resolution uses the saved OpenCode endpoint.

Screenshots

OpenCode endpoint selection in setup

OpenCode endpoint switching in existing account edit

Verification

• pnpm run lint — passed
• pnpm run check:circular — failed due to pre-existing cycle outside this diff:
  • api/tauri/session/index.ts > util/session/sessionDispatch.ts
• cargo clippy --all-targets -- -D warnings — failed due to pre-existing warnings outside changed files
• pnpm exec eslint src/modules/MainApp/Integrations/KeyVault/hooks/useKeyVaultPage.ts src/modules/MainApp/Integrations/KeyVault/Accounts/Table/AccountInlineEditSection.tsx src/modules/MainApp/Integrations/KeyVault/Accounts/Table/AccountInlineExpandedCard.tsx src/modules/MainApp/Integrations/KeyVault/Accounts/Table/MyAccountsTableSection.tsx src/modules/MainApp/Integrations/KeyVault/Table/AccountsTable.tsx src/scaffold/WizardSystem/variants/KeyVault/hooks/useApiSetupTokenDetection.ts src/scaffold/WizardSystem/variants/KeyVault/components/KeySelectionModal.tsx src/scaffold/WizardSystem/variants/KeyVault/components/setup/GenericSetup.tsx — passed
• cargo test -p key_vault opencode — passed
• rustfmt --edition 2021 --check crates/key-vault/src/commands/validate.rs crates/key-vault/src/auto_detect/opencode.rs crates/key-vault/src/provider_config.rs crates/agent-core/src/core/providers/registry.rs — passed
• Husky pre-commit hook passed