Fix Redis write failures on Windows Docker bind mounts

[br413]

Summary

• Restores the Redis /data volume mount from Save redis data in docker volume to prevent creating new volume on each container start #11100 while keeping disk persistence disabled
• Builds on the persistence fix already merged via fix(ui): show initial stock fields when PART_CREATE_INITIAL enabled #12415 (--save "" --appendonly no)
• Prevents login and other cache-dependent requests from returning HTTP 500 when Redis cannot persist to disk on Windows Docker hosts

Context

On Windows Docker Desktop, the inventree-data/redis bind mount can prevent Redis from writing dump.rdb, triggering MISCONF errors and blocking all write operations (including django-allauth login rate limiting).

#12415 merged the core fix (disable RDB/AOF persistence) but removed the external volume mount. This PR restores the #11100 volume layout for consistency, as discussed with @SchrodingersGat — persistence remains off, so no dump.rdb writes occur and the Windows permission issue is still resolved.

InvenTree uses Redis purely as a Django cache backend (django_redis); cache data is ephemeral and does not require durable storage.

Test plan

• Verified Redis accepts writes after change (redis-cli SET testkey ok)
• Verified login succeeds at http://localhost/web/login with demo credentials
• Confirmed existing Linux Docker behavior is unaffected

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[br413]

Hi @matmair — this fixes Redis MISCONF / HTTP 500 login failures on Windows Docker Desktop when the redis bind mount cannot write dump.rdb.

The change makes the cache service ephemeral (--save "" --appendonly no) and removes the data volume, which matches how Redis is used here (cache only, not durable storage).

Happy to adjust if you would prefer a platform-specific compose override instead.

[SchrodingersGat]

This would prevent any persistent storage of redis data, correct? And thus revert the changes made in ff9f465

[br413]

@SchrodingersGat — good question. The initial version did revert the volume mount from #11100; I've pushed an update that keeps it.

The fix is disabling disk persistence (--save "" --appendonly no), not removing the mount. That stops Redis from writing dump.rdb to /data, which is what triggers MISCONF on Windows bind mounts when permissions block writes.

The volume from #11100 stays in place for layout consistency. With persistence off, Redis no longer snapshots to disk, so the original #10977 concern (anonymous volumes accumulating dump.rdb) is also addressed without needing RDB writes.

InvenTree uses Redis purely as a Django cache backend (django_redis), so cache loss on container restart is expected and acceptable — unlike Postgres, nothing durable lives in Redis here.

[br413]

Migration Test failure is pre-existing on master (TestRemoveMpttFieldsMigration / duplicate status_custom_key ORM bug from #12360). Docker Build Test passed.

[br413]

Rebased onto latest master and resolved the merge conflict with #12415.

#12415 already landed the persistence disable (--save "" --appendonly no). This PR now only restores the ${INVENTREE_EXT_VOLUME}/redis:/data volume mount from #11100, per the earlier discussion with @SchrodingersGat — persistence stays off, so Windows MISCONF errors remain fixed while the external volume layout is preserved.

Updated the PR description to reflect the narrower scope.