chore: configure Claude Code datum plugins

Add .claude/settings.json to enable datum-cloud plugins automatically.
This configures the datum-claude-code-plugins marketplace and enables
the datum-platform and datum-gtm plugins.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: scotwells

.claude/settings.json

@@ -0,0 +1,14 @@
+{
+  "extraKnownMarketplaces": {
+    "datum-claude-code-plugins": {
+      "source": {
+        "source": "github",
+        "repo": "datum-cloud/claude-code-plugins"
+      }
+    }
+  },
+  "enabledPlugins": {
+    "datum-platform@datum-claude-code-plugins": true,
+    "datum-gtm@datum-claude-code-plugins": true
+  }
+}