Bank System

### Added
- Added configurable item storage page count per player
- Added configurable item storage slot count per page
- Added `/bankslots <player> <size>`
- Added `/bankreload`
- Added a dedicated admin workflow for item storage management
- Added readable player data support with player name stored in bank JSON files
- Added readable player bank filenames using `PlayerName--uuid.json`

### Changed
- Item storage size is now fully configurable through JSON and admin commands
- Player bank progression is now controlled explicitly instead of being passively increased by permission-based logic
- Default storage can now stay limited for all players until upgraded manually or through future server systems
- Save/load logic for item storage was reworked to support custom page counts and custom slot counts safely
- Storage reload behavior was improved so JSON edits can be applied without restarting the server
- Admin commands are now intended for operator-level usage only

### Improved
- Improved persistence structure for item storage data
- Improved compatibility with manual JSON editing
- Improved safety when reducing slot count so items are not lost if higher slots are still occupied
- Improved readability of stored player bank files
- Improved long-term support for progression systems such as shop-based page unlocks

### Notes
- The item storage UI already existed in 1.4.0 and remains the main bank interface
- This update focuses mainly on configurability, admin control, persistence, and progression support