Time-aware agents and scheduled follow-ups

Agents can now reason about real-world time without guessing from their model cutoff or relying on timestamps pasted into prompts.

• Built-in time tools. get_current_time, convert_time, and time_difference handle IANA timezones and daylight-saving changes. set_timezone can remember an end user's timezone for the current conversation.
• Elapsed-time context. Enable temporal.injectElapsed when an agent should notice that minutes, hours, or days have passed between messages. The injected context uses the conversation timezone, then the agent default, then UTC.
• Self-scheduled follow-ups. The set_reminder tool creates a one-time scheduled run for the current agent using an absolute time or a relative delay. When it fires, the agent receives the follow-up message and can act through its configured tools.

The temporal tools are platform-executed, so they do not need a model-provider key or a separate calendar integration.