feat(redis): add key statistics tracking for database browser

[Abeautifulsnow]

Background Description

Add key statistics functionality to the Redis database browser to display the number of loaded keys / total number of keys,
and update it in real-time during dynamic loading, deletion, and flushing.

Modifications

• Add a RedisDatabaseInfo struct (db + keys) to replace the original Vec<u32>
• list_databases returns the key count for each db (parsing INFO keyspace)
• scan_keys_page adds a DBSIZE call to obtain total_keys
• The frontend TreeNode adds loadedKeyCount / totalKeyCount fields
• The tree node label dynamically displays the db0 (loaded/total) format
• Add updateRedisDbKeyStats to update statistics during loading/deletion/flushing

[t8y2]

✅ Well Done

• Clean architecture: Backend returns RedisDatabaseInfo { db, keys } from INFO keyspace parsing, and total_keys from DBSIZE — both O(1) Redis commands, so no performance concern.
• Smart delta-based updates: updateRedisDbKeyStats supports loaded, total, and totalDelta modes, with Math.max(0, ...) to prevent negative counts. This elegantly handles delete (single and bulk) and flush scenarios without re-querying Redis.
• Correct search mode handling: When in search mode, loaded is passed as undefined so loadedKeyCount isn't corrupted by filtered results.
• Type consistency across the stack: RedisDatabaseInfo is defined in Rust, mirrored in TypeScript (tauri.ts), and properly re-exported through the API layer.
• redisDbLabel helper is clean and handles the totalKeyCount == null edge case gracefully.
• Backward compatible: loadedKeyCount and totalKeyCount are optional on TreeNode, so existing non-Redis tree nodes are unaffected.

LGTM! 🎉