docs: add a reusable terminal smoke-test checklist

[jasonsuhari]

Problem

Terminal compatibility reports are most useful when they capture the same launch, input, resize, mouse, copy, and shutdown evidence. Today contributors have no reusable smoke-test checklist, so reports are difficult to compare across Windows, Linux, macOS, terminals, shells, and multiplexers.

Requested behavior

Add docs/TERMINAL_SMOKE_TEST.md with a concise manual checklist and a copyable report template. Link it from CONTRIBUTING.md and use it to record one real terminal/OS test result in the pull request description.

Likely files

• docs/TERMINAL_SMOKE_TEST.md (new)
• CONTRIBUTING.md

Acceptance checks

• The checklist covers version, OS, architecture, host terminal, shell/profile, and exact launch command.
• It checks first launch, keyboard input, selected-pane routing, resize, scroll, mouse selection/copy, worktrees when available, pane restart, and clean quit.
• Unsupported environments and the current single-process limitation are not presented as bugs.
• The report template avoids credentials and unnecessary local paths.
• One completed test report is included in the pull request description, not committed with personal machine details.

Validation

• Run git diff --check.
• Follow the checklist once on any supported terminal and attach the sanitized result to the pull request.
• Confirm every local Markdown link resolves.

Scope and mentoring

Expected size: small, documentation plus one manual test. No Rust changes are required. Comment with the OS and terminal you can test; the maintainer will help distinguish expected limitations from bugs.