fix(data): drop unique index on lists.name (allow duplicate list names)

The startup-race hardening added a global unique index on lists.name, but
duplicate list names are legitimate and the index broke 8 Worker tests that
seed same-named lists. The seeder race is already handled by the atomic
INSERT...WHERE NOT EXISTS, so the index is redundant. Keep the de-dup migration
step, remove the unique index from config, migration and model snapshot.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/ClaudeDo.Data/Migrations/ClaudeDoDbContextModelSnapshot.cs

@@ -211,10 +211,6 @@ namespace ClaudeDo.Data.Migrations
 
                     b.HasKey("Id");
 
-                    b.HasIndex("Name")
-                        .IsUnique()
-                        .HasDatabaseName("idx_lists_name");
-
                     b.HasIndex("SortOrder")
                         .HasDatabaseName("idx_lists_sort");