Implement the full lifecycle management for MongoDB connections, covering UI, state management, and backend integration.

Scope

• Database type picker: Add MongoDB (with logo) to the 'Add New Connection' picker alongside ElasticSearch and DynamoDB
• Connection form: Create mongodb-connect-dialog.vue with fields for connection name, MongoDB URI (mongodb:// / mongodb+srv://), host/port, username, password, auth source, auth mechanism, database name, and TLS options — with validation via vee-validate + zod
• Test Connection: Verify MongoDB connectivity before saving (backed by a new Tauri Rust command using the mongodb crate)
• Persist connections: Save/load MongoDB connections in Pinia store (connectionStore.ts) and the Tauri store layer
• Connection list: Display MongoDB connections in the connection list with a MongoDB logo badge; support connecting, editing, and removing (with confirmation dialog)
• Backend (Rust): Create src-tauri/src/mongo_client.rs with Tauri commands for mongo_test_connection, register in main.rs, add mongodb crate to Cargo.toml
• Types: Add DatabaseType.MONGODB, MongoDBConnection, MongoCollection types in connectionStore.ts, extend Connection union
• i18n: Add all MongoDB connection strings to enUS.ts and zhCN.ts

Key files to create/modify

• src-tauri/src/mongo_client.rs (new)
• src-tauri/src/main.rs
• src-tauri/Cargo.toml
• src/views/connect/components/mongodb-connect-dialog.vue (new)
• src/views/connect/components/connect-list.vue
• src/store/connectionStore.ts
• src/datasources/mongoApi.ts (new)
• src/assets/svg/mongodb.svg (new)
• src/lang/enUS.ts, src/lang/zhCN.ts

Acceptance criteria

• User can select MongoDB from the database type picker
• User can fill, test, and save a MongoDB connection
• MongoDB connections appear in the connection list with the correct logo
• User can edit and remove MongoDB connections
• Backend verifies connectivity via Tauri command
• feature toggle implemented and connection item hidden in production

Parent issue: #112