feat(graph/construction): implement TaskGraph construction methods
- fromTasks: bulk import via serialized blob, orphan nodes for dangling refs,
DuplicateNodeError for duplicates, edge dedup, null→undefined stripping
- fromRecords: strict validation (TaskNotFoundError for dangling refs,
DuplicateEdgeError for duplicate edges), per-edge qualityRetention
- fromJSON: TypeBox Value.Check validation, InvalidInputError on schema failure,
orphan nodes preserved
- addTask: throws DuplicateNodeError if ID exists
- addDependency: throws TaskNotFoundError/DuplicateEdgeError, deterministic
edge keys per ADR-006, default qualityRetention 0.9
- taskInputToNodeAttrs: strips null→undefined for categorical fields,
drops non-graph fields (tags, assignee, due, created, modified)
- 47 new unit tests (304 total, all passing)
glm-5.1
8d384a7b3e