feat(source-manager): bulk verify/reject API for verification queue

[jonesrussell]

Context

Depends on #328. When reviewing many records, acting one-at-a-time is slow. Reviewers need bulk actions.

Requirements

• POST /api/v1/verification/bulk-verify — accept array of {type, id} pairs
• POST /api/v1/verification/bulk-reject — same format
• Transaction-safe (all-or-nothing)
• Dashboard "select all" checkbox + bulk action buttons

API

POST /api/v1/verification/bulk-verify
POST /api/v1/verification/bulk-reject

Body: {"items": [{"type": "person", "id": "uuid"}, {"type": "band_office", "id": "uuid"}]}

Acceptance Criteria

• Bulk endpoints added to source-manager
• Dashboard has checkbox selection and bulk action buttons
• Error handling for partial failures