feat(app): add clone repository from URL to new project dialog

[Ekaanth]

Issue for this PR

#29723

Type of change

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

What does this PR do?

Adds the ability to clone a Git repository from a URL directly within the new project dialog, instead of only supporting opening a local folder.

Frontend (packages/app):

• New DialogNewProject component with a tabbed interface (GitHub URL / Local folder)
• GitHub tab: URL input field, destination directory picker, and clone button with loading/error states
• Folder tab: existing folder-open flow preserved as a tab

Backend (packages/opencode):

• Project.clone effect that runs git clone with the given URL and destination, validates git is installed, derives the repo name from the URL, and checks the target directory doesn't already exist
• CloneError tagged error for clone failures
• New POST /project/clone HTTP endpoint that delegates to Project.clone

i18n: Added translation keys for all 19 supported languages for the new dialog labels (URL label, destination, clone button, cloning state, error messages, folder tab text).

How did you verify your code works?

• Manually tested the dialog UI, switching between GitHub and Folder tabs
• Tested cloning a public repository via URL and confirming the session opens in the cloned directory
• Verified error handling: empty URL, empty destination, already-existing target directory, and invalid URL all surface appropriate error messages

Screenshots / recordings

Screen.Recording.2026-05-29.at.10.33.55.mov

Checklist

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

[github-actions]

Hey! Your PR title Add clone repository from URL to new project dialog 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]

Thanks for updating your PR! It now meets our contributing guidelines. 👍