fix(sqlite): emit inline foreign keys, bare-name default schema, direct exec

SQLite can't ALTER TABLE ADD CONSTRAINT, so foreign keys are now written
as inline FOREIGN KEY clauses in CREATE TABLE instead of commented-out
ALTER statements. The default schema (public/main) now produces bare
table names instead of a "public_" prefix; other schemas are still
prefixed to avoid collisions. Also adds direct-to-file execution: the
sqlite writer can now apply generated DDL straight to a .db file via
Metadata["connection_string"], wired into `relspec merge --output-conn`.

pkg/writers/sqlite/templates.go

@@ -40,10 +40,22 @@ func NewTemplateExecutor(opts *writers.WriterOptions) (*TemplateExecutor, error)
 
 // TableTemplateData contains data for table template
 type TableTemplateData struct {
-	Schema     string
-	Name       string
-	Columns    []*models.Column
-	PrimaryKey *models.Constraint
+	Schema      string
+	Name        string
+	Columns     []*models.Column
+	PrimaryKey  *models.Constraint
+	ForeignKeys []ForeignKeyTemplateData
+}
+
+// ForeignKeyTemplateData contains data for an inline FOREIGN KEY clause
+type ForeignKeyTemplateData struct {
+	Name           string
+	Columns        []string
+	ForeignSchema  string
+	ForeignTable   string
+	ForeignColumns []string
+	OnDelete       string
+	OnUpdate       string
 }
 
 // IndexTemplateData contains data for index template
@@ -120,16 +132,6 @@ func (te *TemplateExecutor) ExecuteCreateCheckConstraint(data ConstraintTemplate
 	return buf.String(), nil
 }
 
-// ExecuteCreateForeignKey executes the create foreign key template
-func (te *TemplateExecutor) ExecuteCreateForeignKey(data ConstraintTemplateData) (string, error) {
-	var buf bytes.Buffer
-	err := te.templates.ExecuteTemplate(&buf, "create_foreign_key.tmpl", data)
-	if err != nil {
-		return "", fmt.Errorf("failed to execute create_foreign_key template: %w", err)
-	}
-	return buf.String(), nil
-}
-
 // Helper functions to build template data from models
 
 // BuildTableTemplateData builds TableTemplateData from a models.Table
@@ -162,11 +164,35 @@ func BuildTableTemplateData(schema string, table *models.Table) TableTemplateDat
 		}
 	}
 
+	// Collect foreign keys for inline FOREIGN KEY clauses
+	var fks []ForeignKeyTemplateData
+	for _, constraint := range sortConstraints(table.Constraints) {
+		if constraint.Type != models.ForeignKeyConstraint {
+			continue
+		}
+
+		refSchema := tableSchemaName(constraint.ReferencedSchema)
+		if refSchema == "" {
+			refSchema = schema
+		}
+
+		fks = append(fks, ForeignKeyTemplateData{
+			Name:           constraint.Name,
+			Columns:        constraint.Columns,
+			ForeignSchema:  refSchema,
+			ForeignTable:   constraint.ReferencedTable,
+			ForeignColumns: constraint.ReferencedColumns,
+			OnDelete:       constraint.OnDelete,
+			OnUpdate:       constraint.OnUpdate,
+		})
+	}
+
 	return TableTemplateData{
-		Schema:     schema,
-		Name:       table.Name,
-		Columns:    columns,
-		PrimaryKey: pk,
+		Schema:      schema,
+		Name:        table.Name,
+		Columns:     columns,
+		PrimaryKey:  pk,
+		ForeignKeys: fks,
 	}
 }