Add Software Updates tab

[bburda]

Summary

Add a Software Updates tab showing update list and status tracking.

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Proposed solution (optional)

• New UpdatesTab component
• List updates via GET /{entity_type}/{entity_id}/updates
• Register new update via POST /{entity_type}/{entity_id}/updates
• View update details and status
• Track update lifecycle: prepare -> execute -> automated
• Status polling for active updates

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Additional context (optional)

Depends on sovd_web_ui#42 (client migration). Gateway has 8 SOVD-compliant software update endpoints since v0.3.0.