Revamp mobile model picker with search and favorites

[ronak-guliani]

What does this PR do?

This PR revamps the mobile model picker into a centered modal with searchable, all-model browsing instead of the old anchored provider-section dialog. It adds per-model favorite and remove/restore actions, and favorites are sorted to the top for quicker access. It also persists favorites and removed models in settings storage so the picker state survives app restarts and provider refreshes.

How did you verify your code works?

I reviewed the branch diff against origin/dev and validated the picker and settings state flow directly in code for select, favorite, remove, restore, and default paths. Full typecheck could not run in this workspace because Expo base tsconfig/dependencies are not available locally.

[github-actions]

Hey! Your PR title Revamp mobile model picker with search and favorites 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.