fix(opencode): preserve model favorites on startup

[leeweisern]

Fixes #8375

Summary

• defer model.json writes until model state is ready to avoid overwriting saved favorites
• merge and normalize persisted recents/favorites/variants with in-memory state on load

Root Cause

Race condition in local.tsx: save() can run before model.json is loaded, writing empty favorites to disk.

Changes

• Add pendingSave flag to queue writes until ready
• Add isModelEntry, normalizeModelList, normalizeVariant helpers for defensive parsing
• Merge loaded state with in-memory state (preserves early user actions)
• Flush queued save after file load completes

[github-actions]

Hey! Your PR title Fix favorites persistence on startup doesn't follow conventional commit format.

Please update it to start with one of:

• feat: or feat(scope): new feature
• fix: or fix(scope): bug fix
• docs: or docs(scope): documentation changes
• chore: or chore(scope): maintenance tasks
• refactor: or refactor(scope): code refactoring
• test: or test(scope): adding or updating tests

Where scope is the package name (e.g., app, desktop, opencode).

See CONTRIBUTING.md for details.

[github-actions]

The following comment was made by an LLM, it may be inaccurate:

No duplicate PRs found

[github-actions]

Thanks for your contribution!

This PR doesn't have a linked issue. All PRs must reference an existing issue.

Please:

1. Open an issue describing the bug/feature (if one doesn't exist)
2. Add Fixes #<number> or Closes #<number> to this PR description

See CONTRIBUTING.md for details.

[leeweisern]

I have saved favourite models, but new updates overwrites them.