feat(ui): add relationship management features in schema editor

- Implement functionality to create, update, delete, and view relationships between tables.
- Introduce new UI screens for managing relationships, including forms for adding and editing relationships.
- Enhance table editor with navigation to relationship management.
- Ensure relationships are displayed in a structured table format for better usability.

pkg/writers/doc.go

@@ -0,0 +1,67 @@
+// Package writers provides interfaces and implementations for writing database schemas
+// to various output formats and destinations.
+//
+// # Overview
+//
+// The writers package defines a common Writer interface that all format-specific writers
+// implement. This allows RelSpec to export database schemas to multiple formats including:
+//   - SQL schema files (PostgreSQL, SQLite)
+//   - Schema definition files (DBML, DCTX, DrawDB, GraphQL)
+//   - ORM model files (GORM, Bun, Drizzle, Prisma, TypeORM)
+//   - Data interchange formats (JSON, YAML)
+//
+// # Architecture
+//
+// Each writer implementation is located in its own subpackage (e.g., pkg/writers/dbml,
+// pkg/writers/pgsql) and implements the Writer interface, supporting three levels of
+// granularity:
+//   - WriteDatabase() - Write complete database with all schemas
+//   - WriteSchema() - Write single schema with all tables
+//   - WriteTable() - Write single table with all columns and metadata
+//
+// # Usage
+//
+// Writers are instantiated with WriterOptions containing destination-specific configuration:
+//
+//	// Write to file
+//	writer := dbml.NewWriter(&writers.WriterOptions{
+//	    OutputPath: "schema.dbml",
+//	})
+//	err := writer.WriteDatabase(db)
+//
+//	// Write ORM models with package name
+//	writer := gorm.NewWriter(&writers.WriterOptions{
+//	    OutputPath:  "./models",
+//	    PackageName: "models",
+//	})
+//	err := writer.WriteDatabase(db)
+//
+//	// Write with schema flattening for SQLite
+//	writer := sqlite.NewWriter(&writers.WriterOptions{
+//	    OutputPath:    "schema.sql",
+//	    FlattenSchema: true,
+//	})
+//	err := writer.WriteDatabase(db)
+//
+// # Schema Flattening
+//
+// The FlattenSchema option controls how schema-qualified table names are handled:
+//   - false (default): Uses dot notation (schema.table)
+//   - true: Joins with underscore (schema_table), useful for SQLite
+//
+// # Supported Formats
+//
+//   - dbml: Database Markup Language files
+//   - dctx: DCTX schema files
+//   - drawdb: DrawDB JSON format
+//   - graphql: GraphQL schema definition language
+//   - json: JSON database schema
+//   - yaml: YAML database schema
+//   - gorm: Go GORM model structs
+//   - bun: Go Bun model structs
+//   - drizzle: TypeScript Drizzle ORM schemas
+//   - prisma: Prisma schema language
+//   - typeorm: TypeScript TypeORM entities
+//   - pgsql: PostgreSQL SQL schema
+//   - sqlite: SQLite SQL schema with automatic flattening
+package writers