MUL-6632: add status and priority filters to Inbox (#7497)

* feat(inbox): add status and priority filters

Co-authored-by: multica-agent <github@multica.ai>

* fix(inbox): degrade filters for legacy backends

Co-authored-by: multica-agent <github@multica.ai>

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Co-authored-by: J <bohan@devv.ai>
Co-authored-by: multica-agent <github@multica.ai>