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;

apps/server/db/schema.ts

@@ -339,7 +339,7 @@ export const changeSetEntries = sqliteTable('change_set_entries', {
   changeSetId: text('change_set_id')
     .notNull()
     .references(() => changeSets.id, { onDelete: 'cascade' }),
-  entityType: text('entity_type', { enum: ['page', 'phase', 'task', 'phase_dependency'] }).notNull(),
+  entityType: text('entity_type', { enum: ['page', 'phase', 'task', 'phase_dependency', 'task_dependency'] }).notNull(),
   entityId: text('entity_id').notNull(),
   action: text('action', { enum: ['create', 'update', 'delete'] }).notNull(),
   previousState: text('previous_state'), // JSON snapshot, null for creates