feat: plan-centric reconcile wiring (Steps 5-6)

[bdchatham]

Summary

Wires the plan foundations from #87 into the actual reconcile loop. This is the behavioral change that makes Plan the central abstraction across all SeiNode phases.

• Phase-aware BuildPlan: Init plans now include ensure-data-pvc, apply-statefulset, apply-service before sidecar tasks. All plans set TargetPhase/FailedPhase. Running phase builds a convergence plan (apply-statefulset + apply-service).
• Mutating ForNode: ForNode(node) error resumes active plans or builds new ones, stamping directly onto node.Status.Plan. No more (NodePlanner, error) return.
• Simplified reconcile loop: ensureNodeFinalizer → reconcilePeers → ForNode → persist plan → ExecutePlan → emit metrics → reconcileRunningTasks. The phase switch, reconcilePending, reconcileInitializing, reconcileRunning, transitionPhase, and all direct resource creation methods are deleted.
• Bootstrap plans: ensure-data-pvc prepended at start, apply-statefulset + apply-service inserted after teardown-bootstrap (preserving RWO PVC constraint).
• Genesis plans: Infrastructure tasks prepended before ceremony tasks.

What changed in the reconcile loop

Before (6 code paths):

ForNode → Validate → reconcilePeers → ensureNodeDataPVC → switch phase {
  Pending: reconcilePending (build plan, transition)
  Initializing: reconcileInitializing (special-case STS/SVC, ExecutePlan, manual transition)
  Running: reconcileRunning (direct STS/SVC SSA, runtime tasks)
}

After (1 linear path):

ensureNodeFinalizer → reconcilePeers → ForNode → persist plan → ExecutePlan → emit metrics → reconcileRunningTasks

Test plan

• make build — compiles cleanly
• make test — all tests pass (80.5% controller coverage)
• make lint — zero issues
• Review: ForNode plan persistence flow (patch base captured before mutation)
• Review: Bootstrap plan task ordering (ensure-data-pvc → bootstrap → teardown → apply-statefulset)
• Review: Convergence plan lifecycle (built for Running, nilled on completion)

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