[codex] Improve XP3 viewer previews

[fangbm]

Summary

• Detect compiled Kirikiri TJS bytecode in XP3 viewer previews and show a concise bytecode summary instead of attempting to render it as text.
• Extract a small set of UTF-16 string constants from TJS bytecode when available.
• Treat .tlg entries as texture assets so external XP3 plugins can return preview-decodable image bytes for those resources.

Notes

No version numbers were changed.

Validation

• cargo fmt --all -- --check
• cargo test -p suzu-xp3-viewer