Replace unit test with endtoend test for DuckDB

Changes:
- Remove unit test from internal/engine/duckdb/duckdb_test.go
- Generate expected output for examples/duckdb/ (endtoend test will use this)
- Update sqlc.yaml to work without analyzer (catalog-based mode)
- Add generated Go code (db.go, models.go, query.sql.go)

The DuckDB example will now be tested automatically by TestExamples
in internal/endtoend/endtoend_test.go when running with --tags=examples.

Note: Analyzer disabled for now as database/sql can't execute parameterized
queries without values. Catalog-based type inference works correctly.

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

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

examples/duckdb/sqlc.yaml

@@ -6,11 +6,6 @@ sql:
       - "schema.sql"
     queries:
       - "query.sql"
-    database:
-      managed: false
-      uri: ":memory:"
-    analyzer:
-      database: true
     gen:
       go:
         package: "db"