dashboard module fails with "No module named 'smb'" on tentacle/stable and tentacle/edge

## Description
The Ceph dashboard module fails to load on MicroCeph tentacle/stable and
tentacle/edge with:

Module 'dashboard' has failed: No module named 'smb'

## Environment
Tested on both channels:
- Channel: tentacle/stable, Revision: 1734, Ceph version: 20.2.0+snapbe4e67380e
- Channel: tentacle/edge, Revision: 1742, Ceph version: 20.2.0+snap5c2760d8fb

## Steps to reproduce
1. Install MicroCeph on tentacle/stable or tentacle/edge channel
2. Enable the dashboard module: microceph.ceph mgr module enable dashboard
3. Run: microceph.ceph status
4. Observe HEALTH_ERR: Module 'dashboard' has failed: No module named 'smb'

## Root cause
The smb module directory is completely missing from the snap:

$ find /snap/microceph/1742/share/ceph/mgr/smb
(no output - directory does not exist)

$ microceph.ceph mgr module ls | grep smb
(no output - module not present at all)

The dashboard controller unconditionally imports from it:
/snap/microceph/1742/share/ceph/mgr/dashboard/controllers/smb.py

## Upstream fix
Already merged in upstream Ceph:
- PR: https://github.com/ceph/ceph/pull/67510 (merged May 8, 2026)
- Tracker: https://tracker.ceph.com/issues/74268
- Target: v20.2.2

The fix has been merged for over a month but has not been included in
either tentacle/stable (rev 1734) or tentacle/edge (rev 1742).

Please include this fix in the tentacle snap builds.

## Workaround
microceph.ceph mgr module disable dashboard

Start by reviewing the upstream Ceph PR 67510 and comparing the snap contents under /snap/microceph/1742/share/ceph/mgr with the dashboard controller at dashboard/controllers/smb.py. Reproduce the failure with the listed microceph.ceph commands, then verify a new tentacle build contains the smb module and that enabling dashboard no longer reports No module named 'smb'.

Written by the indexing model from the issue text.