fix(chain): truncate ChainStepStatus.Output to prevent etcd limit breach

[dapperdivers]

Problem

ChainStepStatus.Output in chain_types.go:96 is an unbounded string stored in CR status. Knights returning large reports (common in morning briefing with 8 parallel steps) can exceed etcd's 1.5MB object limit, causing status updates to fail and chains to hang.

Impact

• Chain controller hangs when it can't update status
• Morning briefing with 8 verbose knight reports is the most likely trigger
• Silent failure — no error surfaced to the user

Proposed Fix

• Truncate output in status to 32KB with a [truncated] marker
• Store full output in a ConfigMap or NATS KV bucket
• Add outputRef field to ChainStepStatus pointing to the full output location

References

• Architecture review: drafts/roundtable-architecture-review.md (C4)
• File: roundtable-operator/api/v1alpha1/chain_types.go