fix(opencode): support macOS cmd+v image paste in tui

[hernandezsanti]

Issue for this PR

Closes #22194

Type of change

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

What does this PR do?

On macOS, clipboard image paste in the TUI only worked reliably through the existing input_paste path, so cmd+v could miss image attachments depending on the terminal.

This change adds a small probePaste() helper for macOS cmd+v, reuses one clipboard attachment path for both keydown and empty paste events, and avoids double-attaching when the key event and paste event happen back-to-back.

It works because image attachment now happens through the same code path whether the terminal reports paste as ctrl+v, meta/super+v, or an empty paste event.

How did you verify your code works?

• bun test test/cli/cmd/tui/paste-key.test.ts
• bun run typecheck
• manual validation in Ghostty on macOS: copied an image to the clipboard, pressed cmd+v, and confirmed the image attached in the prompt

Screenshots / recordings

N/A for this bug fix.

Checklist

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

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