Add sourcegraph to marketplace

Replace the Google Forms link with the new plugin directory
submission link (https://clau.de/plugin-directory-submission).

https://claude.ai/code/session_01NxRDJKDvFR2d4wC4ppDEDT

Co-authored-by: Claude <noreply@anthropic.com>

.claude-plugin/marketplace.json

@@ -684,6 +684,17 @@
         "url": "https://github.com/semgrep/mcp-marketplace.git"
       },
       "homepage": "https://github.com/semgrep/mcp-marketplace.git"
+    },
+    {
+      "name": "sourcegraph",
+      "description": "Code search and understanding across codebases. Search, read, and trace references across repositories; analyze refactor impact; investigate incidents via commit and diff search; run targeted security sweeps.",
+      "category": "development",
+      "source": {
+        "source": "url",
+        "url": "https://github.com/sourcegraph-community/sourcegraph-claudecode-plugin.git",
+        "sha": "cfe3d44476957b16d1575261bef6b2dc7cb1e0b7"
+      },
+      "homepage": "https://sourcegraph.com"
     }
   ]
 }