fix: Persist and expose task dependencies from detail output

Detail agents define task dependencies in YAML frontmatter but they were
silently dropped — never written to the task_dependencies table. This
caused all tasks to dispatch in parallel regardless of intended ordering,
and the frontend showed no dependency information.

- Add fileIdToDbId mapping and second-pass dependency creation in
  output-handler.ts (mirrors existing phase dependency pattern)
- Add task_dependency to changeset entry entityType enum
- Add listPhaseTaskDependencies tRPC procedure for batch querying
- Wire blockedBy in PhaseDetailPanel and PhaseWithTasks from real data
- Clarify dependency semantics in detail prompt

apps/server/db/repositories/change-set-repository.ts

@@ -16,7 +16,7 @@ export type CreateChangeSetData = {
 };
 
 export type CreateChangeSetEntryData = {
-  entityType: 'page' | 'phase' | 'task' | 'phase_dependency';
+  entityType: 'page' | 'phase' | 'task' | 'phase_dependency' | 'task_dependency';
   entityId: string;
   action: 'create' | 'update' | 'delete';
   previousState?: string | null;