feat(plan): add versioned staged activation

[zzylol]

Summary:

• Add plan_version, activation/expiry metadata, backend compatibility identity, and staged -> active -> draining -> retired lifecycle.
• Stage the complete PhysicalPlan snapshot and activate it with one ArcSwap publication.
• Enforce globally monotonic versions across plan IDs, recheck version at activation time, and prevent the staged-v3/then-v2 downgrade race.
• Keep staged plans and observable lifecycle statuses under one mutex so lifecycle transitions are consistent.
• Rebased on the node-ID physical DAG in feat(query): execute authoritative QueryPlan #472.

Verification:

• cargo check -p control_plane -p data_plane
• activation lifecycle targeted tests pass, including cross-plan downgrade regression
• BackendPlan wire/validation tests: 9 passed
• git diff --check

Stack 2/N. Please do not merge independently of #472.