Tighten continuation message rows

[klopez4212]

Summary

• use uniform 4px top and bottom padding for continuation rows
• keep continuation timestamps top-aligned and remove the thread-only minimum-height gutter
• raise continuation hover actions by 12px
• align virtualized row estimates with the compact layout

Validation

• pnpm test (3,782 tests via pre-push)
• pnpm check
• desktop snapshots

Screenshots

Mention-chip continuation

Emoji continuation

[chatgpt-codex-connector]

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[chatgpt-codex-connector]

💡 Codex Review

Here are some automated review suggestions for this pull request.

Reviewed commit: e7782a48fe

ℹ️ About Codex in GitHub

Your team has set up Codex to review pull requests in this repo. Reviews are triggered when you

• Open a pull request for review
• Mark a draft as ready
• Comment "@codex review".

If Codex has suggestions, it will comment; otherwise it will react with 👍.

Codex can also answer questions or update the PR. Try commenting "@codex address that feedback".