feat: execute projected task nodes independently

[Jinchengawu]

What changed

• Mirror reusable task-node scheduling, persisted TaskContract, workspace-scope narrowing, and acceptance/scope completion gates.
• Support multiple canonical task bindings per Surface while preserving the legacy current-task pointer.
• Update Gateway coordination, Kanban, and Team Loop consumers to count unique task nodes with v1 fallback.
• Keep Open-specific A2A/Profile behavior and distribution boundaries intact; Open does not gain DEV's managed-worker Gateway surface.

Verification

• Open Core, Gateway, and Dashboard typechecks passed.
• Coordination task projection contract passed.
• DEV managed delivery: 9/9; DEV Core: 119/119.
• Framework sync: 18 exact shared files, zero drift.
• DEV E2E delivery gate: 46 PASS / 0 FAIL / 10 WARN (e2e-delivery-gate-20260805_093301.md).