Bridge scheduler handoff context with memory system

[cloga]

Integrate scheduler checkpoint/handoff/yield state with the existing memory/prompt system so scheduler-owned work feels like native chat context.

Scope:

• Build bounded scheduler context packets from task_events
• Inject inherited scheduler context into scheduler-dispatched worker prompts
• Add master resume context API
• Add explicit memory promotion path without automatic memory pollution
• Add tests for prompt injection, bounded context, no automatic memory writes, MCP schemas, and HTTP contracts