snap.microceph.osd.service startup fails with "Operation not permitted"

Startup of snap.microceph.osd.service fails with the following error message left in journalctl:

```
... microceph.osd[1127]: realpath: /var/snap/microceph/1395/..: Operation not permitted
... microceph.osd[1100]: /snap/microceph/1395/commands/osd.start: line 6: /current/run/ceph-osd.pid: No such file or directory
```

The issue seems to be that in https://github.com/canonical/microceph/blob/5f545a9b544a9207739ff96275f6d066796204ad/snapcraft/commands/osd.start#L5 an attempt is made to lookup a path which is outside of the sandbox.

Version information:
```
# Raspberry Pi 5
# uname -a
Linux raspi5-1 6.12.34+rpt-rpi-2712 #1 SMP PREEMPT Debian 1:6.12.34-1+rpt1~bookworm (2025-06-26) aarch64 GNU/Linux
# snap --version
snap version: snap 2.61.4ubuntu0.16.04.1+esm1
snapd 2.61.4ubuntu0.16.04.1+esm1
series 16
debian 12
kernel 6.12.34+rpt-rpi-2712
# snap list
Name Version Rev Tracking Publisher Notes
core 16-2.61.4-20250508 17215 latest/stable canonical✓ core
core20 20250526 2603 latest/stable canonical✓ base
core24 20250618 1059 latest/stable canonical✓ base
microceph 19.2.0+snapab139d4a1f 1395 squid/stable canonical✓ held
```

Reproduce the failure with journalctl and inspect snapcraft/commands/osd.start, especially line 5 where the path lookup occurs. Confirm the service startup behavior and the sandbox boundary; done means snap.microceph.osd.service starts without the reported errors and the expected Ceph OSD PID path is available.

Written by the indexing model from the issue text.