Returns contacts (people and bots) that the authenticated user has communicated with.

Use cases:

• Discover entity IDs for filtering messages by sender via GET /v1/users/:user_id/messages?entity_id=ent_xxx
• Build a contact picker UI
• Show sender details in inbox views

Filtering:

• search: Case-insensitive substring match on contact name, or exact match on an external ID (email address, Slack user ID)
• entity_type: Filter by type (e.g., "person", "bot")
• is_bot: Filter by bot status (true/false)

Pagination (cursor-only):

• limit: Maximum number of contacts per page (default: 50, max: 100)
• cursor: Opaque token from pagination.next_cursor of a prior response. Pass it back unchanged to fetch the next page. Omit on the first page.

The response pagination object contains limit, has_more, and (when has_more=true) next_cursor. There is no offset and no total_count — partners walk pages forward via cursor and use has_more to detect the last page.

Examples:

# List all contacts
GET /v1/users/:user_id/entities

# Search by name or email
GET /v1/users/:user_id/entities?search=john

# Only non-bot contacts
GET /v1/users/:user_id/entities?is_bot=false

# Filter by type
GET /v1/users/:user_id/entities?entity_type=person