Lists: reject duplicate list names within the same tenant

Fixes

• Lists: reject duplicate list names within the same tenant
• Lists endpoints: return camelCase field names
• Suppression and consent endpoints: return camelCase field names
• Outcomes dashboard: byType returns proper types and camelCase
• Deliverability: align totalSent with velocity send count
• Inbound: record-inbound creates thread synchronously
• Agents heartbeat: fix missing required agentId/agentName options
• Webhooks: mask secret on get/update responses
• CLI: correct misleading send propose help text and MCP description
• CLI: batch subcommands no longer blocked by parent required options