docs: update all docs for scrum master agent and sprint-based resume

[shivchander]

Closes #200

Summary

• Update agent count across all docs (README, architecture, index, contributing, ace, self-improvement)
• Add Scrum Master to agent rosters, tables, and architecture diagram
• Replace old factory checkpoint/factory resume CLI references with factory log
• Add crash-resilient resume feature description to README
• Remove hardcoded agent counts ("7 roles", "8 specialists") in favor of flexible language
• Update checkpoint.py → checkpoint_hook.py in module reference tables

7 files changed, +23/-16. Pure documentation — no code changes.

🤖 Generated with Claude Code

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 86.97%. Comparing base (f72f5e6) to head (c658616).

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #204   +/-   ##
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  Coverage   86.97%   86.97%           
=======================================
  Files          51       51           
  Lines        7276     7276           
=======================================
  Hits         6328     6328           
  Misses        948      948           

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[akashgit]

Review

Good intent — mostly mechanical updates. A few issues to fix before merging:

1. Wrong filename rename. docs/architecture.md and docs/contributing.md rename checkpoint.py → checkpoint_hook.py in the module reference tables, but the actual file is still factory/checkpoint.py. The docs will reference a file that doesn't exist.

2. Disconnected diagram node. The .d2 file adds the Scrum Master node but no edges connect it to the CEO or any other node. It'll render as a floating box. Need to add connection lines (e.g., ceo -> agents.scrummaster).

3. Minor inconsistency. docs/contributing.md directory tree says "Agent role prompts (10 roles)" — technically correct (9 specialists + CEO prompt), but every other doc says "nine specialists." Consider "(9 specialists + CEO)" for clarity, or just drop the count.

Fix #1 and #2 and this is good to merge.