[opencode-prs] copy Slack-ready PR summaries

[vvo]

tl;dr; copies any session PR as a Slack-ready link with status and diff counts.

Problem

• Sharing a session PR in Slack requires rebuilding its status, repository, title, link, and diff summary by hand.

Solution

• We add a ⧉ action beside each PR status.
• Copy success or failure appears in an OpenCode toast.

Implementation details

• GitHub metadata now includes additions and deletions.
• Clipboard writes use OSC 52 on both OpenCode versions.
• Output follows :pr-status: owner/repo <url|*title*> +additions -deletions.