feat: add Codex plugin config

.codex-plugin/plugin.json

@@ -0,0 +1,31 @@
+{
+  "name": "spanner",
+  "version": "0.2.6",
+  "description": "Connect and interact with Spanner data using natural language.",
+  "author": {
+    "name": "Google LLC",
+    "email": "data-cloud-ai-integrations@google.com"
+  },
+  "homepage": "https://cloud.google.com/spanner",
+  "repository": "https://github.com/gemini-cli-extensions/spanner",
+  "license": "Apache-2.0",
+  "keywords": [
+    "spanner",
+    "google-cloud",
+    "database"
+  ],
+  "skills": "./skills/",
+  "interface": {
+    "displayName": "Spanner",
+    "shortDescription": "Connect and interact with Spanner data using natural language.",
+    "developerName": "Google LLC",
+    "category": "Database",
+    "capabilities": [
+      "Read",
+      "Write"
+    ],
+    "defaultPrompt": [
+      "You are a senior database engineer and administrator specializing in Spanner. Your goal is to help users explore their Spanner databases, manage schemas, and execute queries effectively."
+    ]
+  }
+}