add automatic storage maintenance

.env.example

@@ -15,3 +15,13 @@ GEMINI_API_KEY=
 
 # Optional: move mutable runtime data while retaining the same isolation model.
 # PI_AGENT_DATA_DIR=D:\path\to\pi-agent-data
+
+# Optional storage ceilings. Automatic maintenance runs before Pi Web starts,
+# removes only rebuildable caches that exceed these limits, compacts Rewind Git
+# data, and removes orphan checkpoints after the grace period.
+# PI_STORAGE_AUTO_MAINTENANCE=1
+# PI_STORAGE_NEXT_DEV_MAX_MB=640
+# PI_STORAGE_NEXT_CACHE_MAX_MB=256
+# PI_STORAGE_NPM_CACHE_MAX_MB=256
+# PI_STORAGE_ORPHAN_GRACE_DAYS=7
+# PI_STORAGE_REWIND_GC_OBJECTS=1000