Add proper endtoend test for DuckDB in testdata

Creates internal/endtoend/testdata/duckdb_basic/duckdb/ with:
- schema.sql: Basic authors table
- query.sql: CRUD operations (GetAuthor, ListAuthors, CreateAuthor, DeleteAuthor)
- sqlc.yaml: DuckDB engine configuration
- go/: Expected generated output (db.go, models.go, query.sql.go)

Test automatically discovered by TestReplay and passes:
✅ TestReplay/base/duckdb_basic/duckdb (0.01s)

This follows the project's endtoend testing conventions where tests
live in internal/endtoend/testdata/ rather than just examples/.

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

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

internal/endtoend/testdata/duckdb_basic/duckdb/query.sql

@@ -0,0 +1,15 @@
+-- name: GetAuthor :one
+SELECT id, name, bio FROM authors
+WHERE id = $1;
+
+-- name: ListAuthors :many
+SELECT id, name, bio FROM authors
+ORDER BY name;
+
+-- name: CreateAuthor :one
+INSERT INTO authors (name, bio)
+VALUES ($1, $2)
+RETURNING id, name, bio;
+
+-- name: DeleteAuthor :exec
+DELETE FROM authors WHERE id = $1;

internal/endtoend/testdata/duckdb_basic/duckdb/schema.sql

@@ -0,0 +1,5 @@
+CREATE TABLE authors (
+    id INTEGER PRIMARY KEY,
+    name VARCHAR NOT NULL,
+    bio TEXT
+);

internal/endtoend/testdata/duckdb_basic/duckdb/sqlc.yaml

@@ -0,0 +1,9 @@
+version: "2"
+sql:
+  - engine: "duckdb"
+    schema: "schema.sql"
+    queries: "query.sql"
+    gen:
+      go:
+        package: "querytest"
+        out: "go"