Fails to migrate a non-encrypted keyring

Nobody has claimed this yet.

I removed the password from my login.keyring in GNOME Keyring (due to various ongoing problems), which causes gnome-keyring-daemon to write the file in text (GLib "keyfile") format, instead of binary format. Currently oo7 version 0.6.0 does not recognize this and fails with:

```
2026-09-17T08:51:45.315958Z DEBUG oo7_daemon::service: Scanning for v0 keyrings in /home/grawity/.local/share/keyrings
2026-09-17T08:51:45.316207Z DEBUG oo7_daemon::service: Found v0 keyring: login
2026-09-17T08:51:45.316338Z DEBUG oo7::file::locked_keyring: Keyring file found, loading its content
2026-09-17T08:51:45.316618Z WARN oo7_daemon::service: Failed to load keyring "/home/grawity/.local/share/keyrings/login.keyring": Portal error File header doesn't match FILE_HEADER Some(
"[keyring]\ndispla",
)
2026-09-17T08:51:45.316677Z INFO oo7_daemon::service: No keyrings discovered in data directory
2026-09-17T08:51:45.316690Z INFO oo7_daemon::service: No default collection found, creating 'Login' keyring
2026-09-17T08:51:45.316765Z DEBUG oo7::file::locked_keyring: Keyring file not found, creating a new one
2026-09-17T08:51:45.316810Z INFO oo7_daemon::service: Created default 'Login' collection (locked)
```

I did not notice any changes in Git since `0.6.0` that would add support for the decrypted format.

The contents of login.keyring look like:

```
[keyring]
display-name=Login
ctime=0
mtime=1441960049
lock-on-idle=false
lock-after=false

[917]
item-type=0
display-name=Remmina: Shore - password
secret=BlahBlahBlahblah
mtime=1768377640
ctime=1768377640

[917:attribute0]
name=filename
type=string
value=/home/grawity/.local/share/remmina/group_rdp_shore_shore-sym.remmina

[917:attribute1]
name=key
type=string
value=password

[917:attribute2]
name=xdg:schema
type=string
value=org.remmina.Password
```

Start in oo7::file::locked_keyring, where the log shows the keyring content is loaded and the FILE_HEADER check fails. Compare the expected binary format with the displayed GLib keyfile format and trace how loaded items are represented. Done means a non-encrypted login.keyring is discovered and its entries load without the shown error.

Written by the indexing model from the issue text.