feat(mcp): add bridge data endpoints for all database types

Add /data/list-tables, /data/describe-table, /data/execute-query
bridge endpoints so the MCP server can delegate queries for non-PG/MySQL
database types (Oracle, H2, Trino, Hive, Neo4j, Cassandra, etc.)
through the DBX desktop app. Direct PG/MySQL connections remain
unchanged. Bump MCP server version to 0.3.0.

mcp/server.json

@@ -6,12 +6,12 @@
     "url": "https://github.com/t8y2/dbx",
     "source": "github"
   },
-  "version": "0.2.1",
+  "version": "0.3.0",
   "packages": [
     {
       "registryType": "npm",
       "identifier": "@dbx-app/mcp-server",
-      "version": "0.2.1",
+      "version": "0.3.0",
       "transport": {
         "type": "stdio"
       }