Add PostgreSQL-compatible version() function

PostgreSQL clients call SELECT version() to check database compatibility.
DuckDB's native version() returns "v1.1.0 ..." which doesn't match
PostgreSQL format. This adds a macro that overrides version() to return
a PostgreSQL-compatible string:

"PostgreSQL 15.0 on x86_64-pc-linux-gnu, compiled by gcc, 64-bit (Duckgres/DuckDB)"

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

Co-Authored-By: Claude Opus 4.5 <[email protected]>

Author: EDsCODE

server/catalog.go

@@ -270,6 +270,9 @@ func initPgCatalog(db *sql.DB) error {
 			END`,
 		// pg_is_in_recovery - check if in recovery mode
 		`CREATE OR REPLACE MACRO pg_is_in_recovery() AS false`,
+		// version - return PostgreSQL-compatible version string
+		// Fivetran and other tools check this to determine compatibility
+		`CREATE OR REPLACE MACRO version() AS 'PostgreSQL 15.0 on x86_64-pc-linux-gnu, compiled by gcc, 64-bit (Duckgres/DuckDB)'`,
 	}
 
 	for _, f := range functions {