Add Replay Lab

[suhaanthayyil]

Summary

• add Replay Lab commands for replaying Entire checkpoints in isolated worktrees and saving reports
• add multi-agent eval runs, report rendering, rankings, and failure/timeout hardening
• expose Replay/Eval in entire labs, expand command help, README usage, changelog, and architecture docs

Supersedes the closed unmerged Replay Lab PR #1334 with a fresh branch based on current origin/main.

Verification

• go test ./cmd/entire/cli -run 'TestReplay|TestEval|TestLabs|TestRootCommandHasReplayAndEval|TestRootHelp' -count=1
• go test ./cmd/entire/cli -count=1
• go test ./...
• go build -o /tmp/entire-replay-release ./cmd/entire
• git diff --check
• smoke-checked /tmp/entire-replay-release labs, replay checkpoint --help, eval run --help, and labs replay

[claude]

Claude Code Review

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