Crash when disk is full while importing

### What Happened?

.

### Steps to Reproduce

0. have less storage free (e.g. 2GB) than the media to import (e.g. 13GB)
1. start photos
2. start import
3. crash

### Expected Behavior

A program should never crash!

Check if enough space is free before starting the import.

### OS Version

6.x (Odin/Jólnir)

### Software Version

Latest release (I have run all updates)

### Log Output

```shell
Terminal:

...
** Message: 17:44:27.299: ImportPage.vala:1723: Skipping import of DSCF6571.RAF: checksum detected in library
** Message: 17:44:27.299: ImportPage.vala:1723: Skipping import of DSCF6578.RAF: checksum detected in library
** Message: 17:44:27.299: ImportPage.vala:1723: Skipping import of DSCF6582.RAF: checksum detected in library

(io.elementary.photos:172599): Gtk-WARNING **: 17:44:27.817: drawing failure for widget 'LibraryWindow': cairo_restore() without matching cairo_save()

** (io.elementary.photos:172599): ERROR **: 17:45:25.090: DatabaseTable.vala:106: add_photo: [13] database or disk is full
Trace/breakpoint trap (core dumped)
```

### Hardware Info

elementary-photos-2.8.0

Start with the import flow in ImportPage.vala and the failure reported at DatabaseTable.vala:106. Reproduce the import with less free storage than the media size, then trace how the disk-full error is handled. Done means the import fails gracefully without crashing when storage is exhausted.

Written by the indexing model from the issue text.