feat(coding-agent): render image blocks in interactive user messages

[AMagicPear]

Summary

• Render image blocks in interactive user messages using the existing TUI Image component.
• Attach clipboard images to the next submitted user message instead of inserting a temp file path.
• Show pending clipboard image attachments in the footer as 1 image attached / N images attached.
• Preserve normal text clipboard paste behavior.

Closes #6563.

Testing

• npm run build
• npm run check
• npx vitest --run test/user-message.test.ts test/interactive-mode-startup-input.test.ts
• ./test.sh with isolated HOME and fd in PATH
• ./pi-test.sh -p --no-session --no-extensions --no-skills --no-context-files --offline --no-tools "Reply with exactly: source-pi-ok"

[github-actions]

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[hrmnjt]

+1

I like the feature; don't know if implementation is worthy of a merge. It removes the need for an extension I asked pi to build for me now. I'll drop extension in favor of a upstream maintained version. Thanks in advance!