Initial commit: gp-mcp server

MCP stdio server for Greenplum 6.x query plan evaluation:
- explain_sql / explain_dbt_model tools
- read-only session enforcement + statement_timeout
- dbt compile integration
- all settings via env vars (no hardcoded defaults)

.env.example

@@ -0,0 +1,26 @@
+# Greenplum connection (required)
+GP_HOST=
+GP_PORT=
+GP_USER=
+GP_PASSWORD=
+GP_DATABASE=
+
+# Greenplum schema search_path (optional, comma-separated)
+GP_SCHEMA=
+
+# dbt project (required for explain_dbt_model)
+DBT_PROJECT_DIR=
+DBT_PROFILES_DIR=
+DBT_TARGET=
+
+# Path to dbt executable (optional, defaults to "dbt" on PATH)
+DBT_EXECUTABLE=
+
+# Statement timeout in milliseconds.
+# STATEMENT_TIMEOUT_MS = default applied to every EXPLAIN ANALYZE.
+# MAX_STATEMENT_TIMEOUT_MS = upper bound; per-call override cannot exceed this.
+STATEMENT_TIMEOUT_MS=
+MAX_STATEMENT_TIMEOUT_MS=
+
+# Logging: DEBUG, INFO, WARNING, ERROR
+LOG_LEVEL=