fix: update dbhub MCP schema to use DSN environment variable

- Changed from DATABASE_URL argument to DSN environment variable
- Updated docker and npx installation methods accordingly
- Maintains compatibility with the dbhub server API

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

Author: zhujian0805

code_assistant_manager/mcp/registry/servers/dbhub.json

@@ -29,11 +29,11 @@
         "run",
         "-i",
         "--rm",
+	"-e",
+	"DSN",
         "bytebase/dbhub",
         "--transport",
-        "stdio",
-        "--dsn",
-        "${DATABASE_URL}"
+        "stdio"
       ]
     },
     "npx": {
@@ -43,14 +43,12 @@
         "-y",
         "@bytebase/dbhub",
         "--transport",
-        "stdio",
-        "--dsn",
-        "${DATABASE_URL}"
+        "stdio"
       ]
     }
   },
   "arguments": {
-    "DATABASE_URL": {
+    "DSN": {
       "description": "The database connection string which includes the user, password, host, port, and database name.",
       "required": true,
       "example": "postgres://user:password@localhost:5432/dbname?sslmode=disable"