fix(orchestrator): PrimaryRepoSyncService.runKbSync cascade records 'completed' on lease-held deferral (cascade sibling of #13785)

Sub of #13755 (heavy-lease deferred-as-completed epic). The cascade sibling of #13785 — which fixed the ProcessSupervisorService kbSync task path; this is the separate PrimaryRepoSyncService cascade spawner, still unfixed.

Problem (V-B-A'd on live source)

PrimaryRepoSyncService.runKbSync (the primary-dev-sync → kbSync cascade, lines 583–601) runs ai:sync-kb via execFileSync and records recordTaskOutcome('kbSync', 'completed', …) + markCompleted('kbSync') on any non-throw (line 586-591). But syncKnowledgeBase.mjs exits 0 on a heavy-maintenance-lease-held deferral — now emitting {deferred:true, reason:'heavy-maintenance-lease-held'} on stdout (post-#13785). The cascade does not parse that stdout, so a lease-held cascade kb-sync is recorded as a false-green completed — the exact telemetry-lie #13785 killed for the task path, surviving in the cascade spawner.

This is the silent-stall failure class of #13755: a deferred cascade kb-sync looks healthy while no embedding happened.

Fix

runKbSync already captures stdout (stdio: ['ignore', 'pipe', 'pipe'], line 576; execFileSync returns it). Parse the child's JSON outcome and record skipped (reasonCode from the outcome) on {deferred:true} instead of completed — mirroring ProcessSupervisorService.classifySuccessfulChildOutcome. The emit side is already done by #13785.

Acceptance

• A lease-held cascade kb-sync records recordTaskOutcome('kbSync', 'skipped', {reasonCode:'heavy-maintenance-lease-held', parent:'primary-dev-sync'}), not completed.
• A real cascade sync still records completed with the embed/delete counts.
• Unit coverage in PrimaryRepoSyncService.spec for both paths.
• Depends on #13785 (the emit side) being merged.

Evidence

L0 (V-B-A of live runKbSync, lines 583-601: try/execFileSync → markCompleted on no-throw, no stdout parse). No existing ticket (dup-sweep clean).

Authored by @neo-opus-vega (Vega), origin session d41446ed.