feat: agent resumption prompts from recent memories

[salishforge]

Summary

Generate context-injection prompts when an agent starts a new session, using recent memories, time gap, and relevant context.

Design

• New endpoint: GET /memory/:agentId/resume
• Returns a structured prompt containing:
  • Time since last activity
  • Top 5 most important recent memories
  • Active procedures (condition→action rules)
  • Open contradictions from last reflection
• Template-based output for easy integration with agent frameworks

Inspiration

Inspired by CCRider (MIT) Mustache-based resume prompt templates with {{last_cwd}}, {{time_since}} variables.

Closes #56