feat(ui): 🎉 Add import and merge database feature

- Introduce a new screen for importing and merging database schemas.
- Implement merge logic to combine schemas, tables, columns, and other objects.
- Add options to skip specific object types during the merge process.
- Update main menu to include the new import and merge option.

README.md

@@ -118,6 +118,55 @@ go install -v git.warky.dev/wdevs/relspecgo/cmd/relspec@latest
 
 ## Usage
 
+### Interactive Schema Editor
+
+```bash
+# Launch interactive editor with a DBML schema
+relspec edit --from dbml --from-path schema.dbml --to dbml --to-path schema.dbml
+
+# Edit PostgreSQL database in place
+relspec edit --from pgsql --from-conn "postgres://user:pass@localhost/mydb" \
+             --to pgsql --to-conn "postgres://user:pass@localhost/mydb"
+
+# Edit JSON schema and save as GORM models
+relspec edit --from json --from-path db.json --to gorm --to-path models/
+```
+
+The `edit` command launches an interactive terminal user interface where you can:
+- Browse and navigate your database structure
+- Create, modify, and delete schemas, tables, and columns
+- Configure column properties, constraints, and relationships
+- Save changes to various formats
+- Import and merge schemas from other databases
+
+### Schema Merging
+
+```bash
+# Merge two JSON schemas (additive merge - adds missing items only)
+relspec merge --target json --target-path base.json \
+              --source json --source-path additions.json \
+              --output json --output-path merged.json
+
+# Merge PostgreSQL database into JSON, skipping specific tables
+relspec merge --target json --target-path current.json \
+              --source pgsql --source-conn "postgres://user:pass@localhost/source_db" \
+              --output json --output-path updated.json \
+              --skip-tables "audit_log,temp_tables"
+
+# Cross-format merge (DBML + YAML → JSON)
+relspec merge --target dbml --target-path base.dbml \
+              --source yaml --source-path additions.yaml \
+              --output json --output-path result.json \
+              --skip-relations --skip-views
+```
+
+The `merge` command combines two database schemas additively:
+- Adds missing schemas, tables, columns, and other objects
+- Never modifies or deletes existing items (safe operation)
+- Supports selective merging with skip options (domains, relations, enums, views, sequences, specific tables)
+- Works across any combination of supported formats
+- Perfect for integrating multiple schema definitions or applying patches
+
 ### Schema Conversion
 
 ```bash