feat: add swarm-common obsidian vault

Add Obsidian vault to the swarm-common virtiofs share for access
from zap VM and other VMs. Contains agent memory, notes, and
infrastructure documentation.

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

swarm-common/obsidian-vault/.obsidian/app.json

@@ -0,0 +1,5 @@
+{
+  "legacyEditor": false,
+  "livePreview": true,
+  "defaultViewMode": "source"
+}