docs: Document Shift+Enter key binding for Alacritty and Tmux

[angelcervera]

Added configuration instructions for Shift+Enter key binding in Alacritty and Tmux.

Issue for this PR

Close #25831

Type of change

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

What does this PR do?

The current doc only explain how to enable Shift+Enter in Windows terminal. This PR add documentation for Alacritty and Tmux.

How did you verify your code works?

Tested locally in my setup.

Screenshots / recordings

No UI

Checklist

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

[github-actions]

Hey! Your PR title Document Shift+Enter key binding for Alacritty and Tmux 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 one potentially related PR:

PR #23430: "fix(app): make prompt submit and newline rebindable"

• fix(app): make prompt submit and newline rebindable #23430
• This PR is related to making key bindings rebindable, which is related to the Shift+Enter functionality being documented in PR docs: Document Shift+Enter key binding for Alacritty and Tmux #25830.

However, PR #23430 appears to be a feature implementation PR, while PR #25830 is purely documentation-focused for existing functionality. They complement each other but aren't duplicates.

No true duplicate documentation PRs were found.

[github-actions]

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