docs: update README and docs for Scrum Master agent and sprint-based resume

[akashgit]

Context

PR #137 merged the sprint-based resume system with a new Scrum Master agent. Several documentation surfaces need updating to reflect the new architecture.

What needs updating

README.md

• Add Scrum Master to the agent roster (now 9 agents, not 8)
• Document factory log CLI command
• Mention crash recovery / sprint resume capability
• Update any architecture diagrams or descriptions that reference agent count

Other docs

• Check docs/ for any references to the old checkpoint-based resume system (factory checkpoint --save, factory checkpoint --clear, ## Resume Context)
• Replace with references to the new event-log + Scrum Master standup approach
• Document factory log <path> <event_type> [--data JSON] [--agent NAME] usage

CLAUDE.md (already done)

• CLAUDE.md was updated in feat: sprint-based resume with scrum master agent #137 — no action needed there

Acceptance criteria

• README reflects 9 agents and lists Scrum Master
• factory log command documented
• No stale references to checkpoint-based resume in docs
• Sprint resume / crash recovery mentioned as a feature