Add vim mode support

[mahersaba]

Issue for this PR

Adding /vim support to OpenCode

Type of change

• Bug fix
• New feature
• Refactor / code improvement
• Documentation

What does this PR do?

Adding a /vim support for vim command, hjkl, 0, $, i, I, dd, D, cw, x.
Adding support for reading the config file and setting the default mode, with /vim mode being off by default and persistent across sessions if changed.

If you paste a large clearly AI generated description here your PR may be IGNORED or CLOSED!

How did you verify your code works?

I test it manually

Screenshots / recordings

It's a text mode changes, not UI.

Checklist

• I have tested my changes locally
• I have not included unrelated changes in this PR

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[github-actions]

This PR doesn't fully meet our contributing guidelines and PR template.

What needs to be fixed:

• No issue referenced. Please add Closes #<number> linking to the relevant issue.

Please edit this PR description to address the above within 2 hours, or it will be automatically closed.

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[github-actions]

Hey! Your PR title Add vim mode support 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:

Based on my search, I found a potentially related PR:

Related PR:

• feat(tui): vim motions in prompt input #12679 - feat(tui): vim motions in prompt input

This PR appears to be related as it also implements vim motions/keybindings for the TUI editor (hjkl, 0, $, etc.). This could be addressing the same feature area as PR #17124, or it may have already implemented some of the functionality you're adding. You should review this PR to understand what vim support already exists and ensure your changes don't duplicate or conflict with it.