Display save status indicator for database changes (saved/unsaved changes)

### Checks

- [x] I have read the Wiki, searched the open issues, and still think this is a new feature.

### Explain the problem clearly and succinctly:

Currently, there is no visual way to determine whether the current database is fully saved or if there are unsaved changes. This can lead to unintentional data loss if users close the app before saving recent modifications.

### Describe the solution you'd like:

A visual indicator (such as an icon or label) in the UI to show the current save status of the database:

- Show a “Saved” status (for example, a green checkmark) when all changes are saved.

- Show an “Unsaved changes” status (for example, a yellow warning icon) if there are any modifications that haven’t been saved yet.
This will help users quickly understand if they need to save their work and reduce the risk of lost data.

### Describe alternatives you've considered:

- Relying on manual discipline to save after every change or edit (prone to mistakes).

- Adding a confirmation dialog on exit if there are unsaved changes (could complement the indicator but not replace it).

### Additional context:

_No response_

Start by locating the Android UI for editing the KeePass database and the existing save and modification flow. Trace how changes become persisted, then determine where a saved or unsaved status can be displayed. Done means the UI distinguishes fully saved data from pending changes and the indicator updates reliably after edits and saves.

Written by the indexing model from the issue text.