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/diff/doc.go

@@ -0,0 +1,43 @@
+// Package diff provides utilities for comparing database schemas and identifying differences.
+//
+// # Overview
+//
+// The diff package compares two database models at various granularity levels (database,
+// schema, table, column) and produces detailed reports of differences including:
+//   - Missing items (present in source but not in target)
+//   - Extra items (present in target but not in source)
+//   - Modified items (present in both but with different properties)
+//
+// # Usage
+//
+// Compare two databases and format the output:
+//
+//	result := diff.CompareDatabases(sourceDB, targetDB)
+//	err := diff.FormatDiff(result, diff.OutputFormatText, os.Stdout)
+//
+// # Output Formats
+//
+// The package supports multiple output formats:
+//   - OutputFormatText: Human-readable text format
+//   - OutputFormatJSON: Structured JSON output
+//   - OutputFormatYAML: Structured YAML output
+//
+// # Comparison Scope
+//
+// The comparison covers:
+//   - Schemas: Name, description, and contents
+//   - Tables: Name, description, and all sub-elements
+//   - Columns: Type, nullability, defaults, constraints
+//   - Indexes: Columns, uniqueness, type
+//   - Constraints: Type, columns, references
+//   - Relationships: Type, from/to tables and columns
+//   - Views: Definition and columns
+//   - Sequences: Start value, increment, min/max values
+//
+// # Use Cases
+//
+//   - Schema migration planning
+//   - Database synchronization verification
+//   - Change tracking and auditing
+//   - CI/CD pipeline validation
+package diff