Decompose architecture into 28 atomic implementation tasks

Break the @alkdev/taskgraph architecture specs into dependency-ordered
implementation tasks across 8 component directories: setup, schema,
error, graph, analysis, cost-benefit, frontmatter, api, and review.
Each task has clear acceptance criteria referencing specific architecture
docs. Three review tasks serve as quality gates at critical junction
points (schemas-and-errors, graph-complete, complete-library). The
dependency graph is validated acyclic with 9 topological levels enabling
significant parallelism across independent work streams.

tasks/implementation/schema/enums.md

@@ -0,0 +1,44 @@
+---
+id: schema/enums
+name: Define TypeBox categorical enum schemas and type aliases
+status: pending
+depends_on:
+  - setup/project-init
+scope: narrow
+risk: trivial
+impact: component
+level: implementation
+---
+
+## Description
+
+Define all categorical enum schemas using `Type.Union([Type.Literal(...)])` pattern per [schemas.md](../../../docs/architecture/schemas.md). Each enum gets a schema constant (PascalCase + `Enum` suffix) and a `Static<typeof>` type alias (PascalCase, no suffix).
+
+The six enums: `TaskScopeEnum`, `TaskRiskEnum`, `TaskImpactEnum`, `TaskLevelEnum`, `TaskPriorityEnum`, `TaskStatusEnum`.
+
+## Acceptance Criteria
+
+- [ ] `src/schema/enums.ts` exports all six enum schemas and their type aliases
+- [ ] Each enum uses `Type.Union([Type.Literal("value"), ...])` pattern per [typebox-patterns.md](../../../docs/research/typebox-patterns.md)
+- [ ] `TaskScopeEnum`: `"single" | "narrow" | "moderate" | "broad" | "system"`
+- [ ] `TaskRiskEnum`: `"trivial" | "low" | "medium" | "high" | "critical"`
+- [ ] `TaskImpactEnum`: `"isolated" | "component" | "phase" | "project"`
+- [ ] `TaskLevelEnum`: `"planning" | "decomposition" | "implementation" | "review" | "research"`
+- [ ] `TaskPriorityEnum`: `"low" | "medium" | "high" | "critical"`
+- [ ] `TaskStatusEnum`: `"pending" | "in-progress" | "completed" | "failed" | "blocked"`
+- [ ] Type aliases derived via `Static<typeof>`: `TaskScope`, `TaskRisk`, `TaskImpact`, `TaskLevel`, `TaskPriority`, `TaskStatus`
+- [ ] Naming convention matches spec: `Enum` suffix on schema constants only, never on type aliases
+- [ ] `src/schema/index.ts` re-exports all schemas and types
+
+## References
+
+- docs/architecture/schemas.md — enum definitions, naming convention
+- docs/research/typebox-patterns.md — TypeBox enum patterns, naming convention
+
+## Notes
+
+> To be filled by implementation agent
+
+## Summary
+
+> To be filled on completion