fix(data-platform): use separate hooks.json file (not inline)

Cherry-pick fix from hotfix/data-platform-hooks to development.
Hooks must be in separate hooks/hooks.json file (auto-discovered),
NOT inline in plugin.json.

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

plugins/data-platform/hooks/hooks.json

@@ -0,0 +1,10 @@
+{
+  "hooks": {
+    "SessionStart": [
+      {
+        "type": "command",
+        "command": "${CLAUDE_PLUGIN_ROOT}/hooks/startup-check.sh"
+      }
+    ]
+  }
+}