feat(10-03): add parallelization config to config.json template

- enabled: Master switch for parallelization
- plan_level: Enable parallel plan execution
- task_level: Enable parallel task execution (future)
- skip_checkpoints: Skip human checkpoints in background mode
- max_concurrent_agents: Limit on concurrent agents (default: 3)
- min_plans_for_parallel: Minimum plans to trigger parallelization (default: 2)

get-shit-done/templates/config.json

@@ -1,6 +1,14 @@
 {
   "mode": "interactive",
   "depth": "standard",
+  "parallelization": {
+    "enabled": true,
+    "plan_level": true,
+    "task_level": false,
+    "skip_checkpoints": true,
+    "max_concurrent_agents": 3,
+    "min_plans_for_parallel": 2
+  },
   "gates": {
     "confirm_project": true,
     "confirm_phases": true,