Extract TUI plugin catalog rendering

[canvrno-oai]

This mechanically extracts the existing TUI plugin catalog and detail popup rendering from chatwidget/plugins.rs into a new chatwidget/plugin_catalog.rs module. plugins.rs now keeps the stateful plugin workflow and orchestration, while plugin_catalog.rs owns the presentation-heavy catalog/detail popup construction and its pure helpers. The goal is to keep plugins.rs focused before later plugin sharing work adds more catalog behavior.

• Moves existing catalog/detail popup builders and related pure helpers into plugin_catalog.rs
• Leaves plugin fetch/state/key handling in plugins.rs
• Adds only minimal sibling-module visibility/import wiring
• Intentionally makes no product behavior or UI changes beyond the code move

[canvrno-oai]

@codex review

[chatgpt-codex-connector]

Codex Review: Didn't find any major issues. Nice work!

Reviewed commit: fb1e5fc430

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