feat(sqlite): add SQLite writer for converting PostgreSQL schemas

- Implement SQLite DDL writer to convert PostgreSQL schemas to SQLite-compatible SQL statements.
- Include automatic schema flattening, type mapping, auto-increment detection, and function translation.
- Add templates for creating tables, indexes, unique constraints, check constraints, and foreign keys.
- Implement tests for writer functionality and data type mapping.

pkg/writers/sqlite/templates/create_check_constraint.tmpl

@@ -0,0 +1,4 @@
+-- Check constraint: {{.Name}}
+-- {{.Expression}}
+-- Note: SQLite supports CHECK constraints in CREATE TABLE or ALTER TABLE ADD CHECK
+-- This must be added manually to the table definition above

pkg/writers/sqlite/templates/create_foreign_key.tmpl

@@ -0,0 +1,6 @@
+-- Foreign key: {{.Name}}
+-- ALTER TABLE {{quote_ident (qualified_table_name .Schema .Table)}} ADD CONSTRAINT {{quote_ident (format_constraint_name .Schema .Table .Name)}}
+--   FOREIGN KEY ({{range $i, $col := .Columns}}{{if $i}}, {{end}}{{quote_ident $col}}{{end}})
+--   REFERENCES {{quote_ident (qualified_table_name .ForeignSchema .ForeignTable)}} ({{range $i, $col := .ForeignColumns}}{{if $i}}, {{end}}{{quote_ident $col}}{{end}})
+--   {{if .OnDelete}}ON DELETE {{.OnDelete}}{{end}}{{if .OnUpdate}} ON UPDATE {{.OnUpdate}}{{end}};
+-- Note: Foreign keys should be defined in CREATE TABLE for better SQLite compatibility

pkg/writers/sqlite/templates/create_index.tmpl

@@ -0,0 +1 @@
+CREATE INDEX {{quote_ident (format_constraint_name .Schema .Table .Name)}} ON {{quote_ident (qualified_table_name .Schema .Table)}} ({{range $i, $col := .Columns}}{{if $i}}, {{end}}{{quote_ident $col}}{{end}});

pkg/writers/sqlite/templates/create_table.tmpl

@@ -0,0 +1,9 @@
+CREATE TABLE {{quote_ident (qualified_table_name .Schema .Name)}} (
+{{- $hasAutoIncrement := false}}
+{{- range $i, $col := .Columns}}{{if $i}},{{end}}
+    {{quote_ident $col.Name}} {{map_type $col.Type}}{{if is_autoincrement $col}}{{$hasAutoIncrement = true}} PRIMARY KEY AUTOINCREMENT{{else}}{{if $col.NotNull}} NOT NULL{{end}}{{if ne (format_default $col) ""}} DEFAULT {{format_default $col}}{{end}}{{end}}
+{{- end}}
+{{- if and .PrimaryKey (not $hasAutoIncrement)}}{{if gt (len .Columns) 0}},{{end}}
+    PRIMARY KEY ({{range $i, $colName := .PrimaryKey.Columns}}{{if $i}}, {{end}}{{quote_ident $colName}}{{end}})
+{{- end}}
+);

pkg/writers/sqlite/templates/create_unique_constraint.tmpl

@@ -0,0 +1 @@
+CREATE UNIQUE INDEX {{quote_ident (format_constraint_name .Schema .Table .Name)}} ON {{quote_ident (qualified_table_name .Schema .Table)}} ({{range $i, $col := .Columns}}{{if $i}}, {{end}}{{quote_ident $col}}{{end}});

pkg/writers/sqlite/templates/pragma_foreign_keys.tmpl

@@ -0,0 +1,2 @@
+-- Enable foreign key constraints
+PRAGMA foreign_keys = ON;