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/analysis/bottlenecks.md

@@ -0,0 +1,38 @@
+---
+id: analysis/bottlenecks
+name: Implement bottlenecks analysis function
+status: pending
+depends_on:
+  - graph/construction
+  - graph/queries
+scope: narrow
+risk: low
+impact: component
+level: implementation
+---
+
+## Description
+
+Implement `bottlenecks(graph: TaskGraph): Array<{ taskId: string; score: number }>` using `graphology-metrics` betweenness centrality. Bottleneck tasks are those on the most shortest paths between other nodes.
+
+## Acceptance Criteria
+
+- [ ] `bottlenecks` returns array of `{ taskId, score }` objects sorted by score descending
+- [ ] Uses `graphology-metrics` betweenness centrality computation
+- [ ] Normalized scores (0.0–1.0 range)
+- [ ] Tasks with score 0 are still included (they're not bottlenecks)
+- [ ] Works on disconnected graphs (betweenness is 0 for disconnected components)
+- [ ] Unit tests: linear chain (middle node has highest betweenness), star graph (center has highest), independent nodes (all zero)
+
+## References
+
+- docs/architecture/api-surface.md — bottlenecks signature
+- docs/architecture/build-distribution.md — graphology-metrics dependency
+
+## Notes
+
+> To be filled by implementation agent
+
+## Summary
+
+> To be filled on completion