[Feat] Add session preview rendering

[samzong]

What's changed?

• Added richer shared session HTML rendering with a reading layout, user navigation, grouped tool logs, markdown/code handling, and model/thinking metadata.
• Added local TUI session preview via v and passes usage metadata through CLI/TUI sharing paths.
• Kept Cloudflare Pages share previews on the configured project domain while validating generated asset size before deploy.

Why

• Make shared session pages easier to read and let users preview the rendered HTML before publishing.

[chatgpt-codex-connector]

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[chatgpt-codex-connector]

Preserve assistant text after leading tool logs

When an assistant message starts with a tool-looking line but also includes normal answer text later in the same message, this branch moves the entire message into pending_tools, so the answer is rendered only inside a collapsed log instead of as visible assistant prose. This regresses the previous line-by-line rendering for mixed messages such as [tool:read]\nHere is the result...; only the tool lines should be grouped, while subsequent prose should remain visible.

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