fix: mount memory-backed emptyDir at /dev/shm for Electron apps

Instead of disabling shared memory usage, mount a proper tmpfs at
/dev/shm so Antigravity (and Chrome) have real shared memory available.
Removes --disable-dev-shm-usage; keeps --no-sandbox (separate issue).

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

chart/values.yaml

@@ -41,6 +41,11 @@ storage:
   size: 32Gi
   className: ceph-filesystem
 
+# Shared memory size — mounted at /dev/shm as a memory-backed emptyDir.
+# Electron apps (Antigravity, Chrome) use /dev/shm for GPU/IPC buffers.
+shm:
+  sizeLimit: 2Gi
+
 resources:
   requests:
     memory: "2Gi"