feat(data): add Idle/Cancelled status, PlanningPhase enum, BlockedByTaskId field

Slice 1 of the worker-state-and-queue-consolidation refactor — additive only,
no caller changes. Introduces the new orthogonal status model:

- TaskStatus gains canonical Idle and Cancelled values; legacy values
  (Manual, Planning, Planned, Draft, Waiting) stay around until slice 6.
- New PlanningPhase enum (None/Active/Finalized) for parent tasks.
- New BlockedByTaskId FK on TaskEntity for sequential chain ordering;
  ON DELETE SET NULL so orphaned children become pickable.
- EF migration adds planning_phase and blocked_by_task_id columns plus
  the idx_tasks_blocked_by index. Also picks up an unrelated drift in
  app_settings.default_permission_mode that had been changed in code
  (commit 14cc9fb) without a migration.

src/ClaudeDo.Data/Migrations/ClaudeDoDbContextModelSnapshot.cs

@@ -84,7 +84,7 @@ namespace ClaudeDo.Data.Migrations
                             DefaultClaudeInstructions = "",
                             DefaultMaxTurns = 100,
                             DefaultModel = "sonnet",
-                            DefaultPermissionMode = "bypassPermissions",
+                            DefaultPermissionMode = "auto",
                             WorktreeAutoCleanupDays = 7,
                             WorktreeAutoCleanupEnabled = false,
                             WorktreeStrategy = "sibling"
@@ -225,6 +225,10 @@ namespace ClaudeDo.Data.Migrations
                         .HasColumnType("TEXT")
                         .HasColumnName("agent_path");
 
+                    b.Property<string>("BlockedByTaskId")
+                        .HasColumnType("TEXT")
+                        .HasColumnName("blocked_by_task_id");
+
                     b.Property<string>("CommitType")
                         .IsRequired()
                         .ValueGeneratedOnAdd()
@@ -285,6 +289,13 @@ namespace ClaudeDo.Data.Migrations
                         .HasColumnType("TEXT")
                         .HasColumnName("planning_finalized_at");
 
+                    b.Property<string>("PlanningPhase")
+                        .IsRequired()
+                        .ValueGeneratedOnAdd()
+                        .HasColumnType("TEXT")
+                        .HasDefaultValue("none")
+                        .HasColumnName("planning_phase");
+
                     b.Property<string>("PlanningSessionId")
                         .HasColumnType("TEXT")
                         .HasColumnName("planning_session_id");
@@ -327,6 +338,9 @@ namespace ClaudeDo.Data.Migrations
 
                     b.HasKey("Id");
 
+                    b.HasIndex("BlockedByTaskId")
+                        .HasDatabaseName("idx_tasks_blocked_by");
+
                     b.HasIndex("ListId")
                         .HasDatabaseName("idx_tasks_list_id");
 
@@ -519,6 +533,11 @@ namespace ClaudeDo.Data.Migrations
 
             modelBuilder.Entity("ClaudeDo.Data.Models.TaskEntity", b =>
                 {
+                    b.HasOne("ClaudeDo.Data.Models.TaskEntity", null)
+                        .WithMany()
+                        .HasForeignKey("BlockedByTaskId")
+                        .OnDelete(DeleteBehavior.SetNull);
+
                     b.HasOne("ClaudeDo.Data.Models.ListEntity", "List")
                         .WithMany("Tasks")
                         .HasForeignKey("ListId")