feat: scoring team resolution, regen image guard, state boundary docs

[JRemitz]

Summary

• Scoring team resolution: new _resolve_scoring_opposing() resolves home/away from event metadata team tag, with fallback to event_type prefix convention
• Regenerate image guard: skip livestream/playlist metadata when regenerate_image_only flag is set in hook context — allows dock to re-generate game thumbnail without creating new livestreams
• Render metadata: pass game creation prompt overrides through to title/description generation
• CLAUDE.md: add Game State Boundary section — plugins must not import reeln-state or touch game.json directly

Test plan

• 290 unit tests passing
• Verify regenerate_image_only skips livestream metadata
• Verify scoring team resolution from metadata["team"] tag

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