Get Project Inbox Counts

Tab + chip counters for the Project Inbox header.

Returns the three tab counters (need_reply / replied / sent) plus available_filters — the dynamic chip list for All replies, where each entry has {key, label, icon, count}. All numbers come from a single SQL helper (:func:api.outreach.db.get_inbox_bucket_counts) so the tab and chip displays never disagree.

Project-wide when campaign=all; scoped to one segment when campaign={segmentId}. Filters with zero leads under the current campaign scope are omitted from available_filters so the chip row stays clean.