Split delivery and execution workflow state

[ZHOUKAILIAN]

Summary

• Split the AGT state model into delivery-workflow.json and execution-workflow.json.
• Add a delivery projector so execution updates derive the user-facing delivery phase/status/blockers without reverse-writing into execution.
• Make CLI status delivery-first, add --from / --from-dir, and keep inspect exposing both workflow layers.
• Preserve existing .agt/config.json values when agt init runs without explicit config flags.
• Audit global paths: task worktree/session-index, migrate, server snapshot, and Web workbench delivery-phase grouping.
• Add the detailed workflow spec in docs/workflow-specs/2026-06-18-delivery-execution-workflow.md.

Verification

• npm run typecheck
• npm test
• npm run build
• python3 -m unittest tests.test_docs
• CLI smoke: default full, --from, no legacy workflow.json
• CLI blocked smoke: delivery phase blocker and reason surfaced
• init smoke: new project defaults to full, existing config is preserved
• task worktree/session-index smoke
• human gate/decision smoke
• migrate blocked + server snapshot smoke