fix: prevent stale duplicate planning tasks from blocking phase completion

Three fixes for phases getting stuck when a detail task crashes and is retried:

1. detailPhase mutation (architect.ts): clean up orphaned pending/in_progress
   detail tasks before creating new ones, preventing duplicates at the source
2. orchestrator recovery: detect and complete stale duplicate planning tasks
   (same category+phase, one completed, one pending)
3. ensureBranch: catch "already exists" TOCTOU race instead of blocking phase

apps/server/trpc/routers/architect.ts

@@ -337,6 +337,14 @@ export function architectProcedures(publicProcedure: ProcedureBuilder) {
           });
         }
 
+        // Clean up orphaned pending/in_progress detail tasks from previous failed attempts
+        const phaseTasks = await taskRepo.findByPhaseId(input.phaseId);
+        for (const t of phaseTasks) {
+          if (t.category === 'detail' && (t.status === 'pending' || t.status === 'in_progress')) {
+            await taskRepo.update(t.id, { status: 'completed', summary: 'Superseded by retry' });
+          }
+        }
+
         const detailTaskName = input.taskName ?? `Detail: ${phase.name}`;
         const task = await taskRepo.create({
           phaseId: phase.id,