AD-801: Build Workflow Canvas MVP

[alph-cmky]

Source: docs/development/task-backlog.md

Milestone: Phase 8: Workflow Canvas and Patch Approval

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AD-801: Build Workflow Canvas MVP

Goal: Provide a visual DAG editor backed by workflow-core.

Files:

• Create apps/web/src/features/workflows/workflow-canvas.tsx
• Create apps/web/src/features/workflows/node-inspector.tsx
• Create apps/web/src/features/workflows/node-palette.tsx

Tasks:

• Support Start, Agent, Tool, Condition, Human Approval, and End nodes.
• Open selected node settings in the right inspector.
• Run validation before saving.
• Commit with message feat: add workflow canvas mvp.

Acceptance Criteria:

• A user can create a valid workflow and see validation errors for invalid DAGs.