Add Triggers tab

[bburda]

Summary

Add a Triggers tab to the entity resource panel with CRUD trigger management, condition display, and SSE event streaming.

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Proposed solution (optional)

• New TriggersTab component
• List triggers via GET /{entity_type}/{entity_id}/triggers
• Create trigger with condition configuration (OnChange, OnChangeTo, EnterRange, LeaveRange)
• View/edit/delete individual triggers
• SSE event stream panel via GET /{entity_type}/{entity_id}/triggers/{trigger_id}/events
• Display trigger status and last-fired timestamp

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Additional context (optional)

Depends on sovd_web_ui#42 (client migration). Gateway supports condition-based triggers with persistent SQLite storage since v0.4.0.