KG: triage workflow for Inspector review flags #428

Part of #386. Runs after a review round, once flags exist.

• One read-only agent per flag diagnoses the cause, with evidence: data error, exporter bug, schema gap or shape gap.
• A second agent tries to refute each diagnosis.
• Confirmed flags are grouped by cause, and each cause gets one fix in its own worktree PR that must pass kg/ci_check.py.
• Data fixes go to the owner as proposed bbqs-mcp calls.