Module: MongoDB Schema & Collection Browsing

[Blankll]

Enable database and collection browsing for MongoDB connections, including schema navigation and basic collection statistics.

Scope

• Database listing: On connection, fetch and display available databases
• Collection listing: List collections for the selected database; allow switching active collection in the toolbar (analogous to ES index selection)
• Collection stats: Display document count, storage size, and average document size for collections
• Toolbar integration: Update the connection/index selector dropdowns to work with MongoDB databases and collections
• Basic auto-completion: Provide collection name auto-completion in the editor (advanced field-level and operator completion is deferred to a future ticket per MongoDB support #112)
• Backend: Add Tauri commands mongo_list_databases, mongo_list_collections, mongo_collection_stats in mongo_client.rs

Key files to create/modify

• src-tauri/src/mongo_client.rs
• src/datasources/mongoApi.ts
• src/store/connectionStore.ts
• src/components/tool-bar.vue
• src/common/monaco/ (completion provider)

Acceptance criteria

• After connecting, user can see a list of databases and their collections
• User can select a collection and it becomes the active context for queries
• Collection stats (count, size) are displayed
• Collection names auto-complete in the editor
• Toolbar dropdowns work for MongoDB database/collection selection

Parent issue: #112
Depends on: Module: MongoDB Query Execution Integration