Add output repository reseed workflow for recreated remotes

[schmoelder]

CADET-RDM has an awkward recovery path when an output repository remote is intentionally deleted and recreated, for example to purge GitHub-hosted Git LFS objects.

Current behavior:

• The project repository metadata still points to the output remote.
• ProjectRepo(...) notices that the local output directory is missing and clones the configured remote.
• If the recreated remote is empty, OutputRepo(...) then fails with FileNotFoundError because output/.cadet-rdm-data.json is missing.
• The useful initialization code exists internally as initialize_output_repo(...), but there is no obvious output-only CLI workflow for this case.

Expected workflow:

CADET-RDM should expose a command such as:

cadetrdm output reseed --remote git@github.com:owner/project_output.git

or:

cadetrdm output init --force

The command should:

1. read project_uuid, output_uuid, the output directory name, and configured output remote from the project repository metadata;
2. create a fresh local output repository with valid CADET-RDM output metadata;
3. add or preserve the configured output remote;
4. optionally push only the fresh main branch;
5. avoid restoring old result branches or old LFS objects.

For this recovery case, the existing project_uuid and output_uuid should be preserved, because the output repository is still the same logical RDM output store.
The remote has only been recreated to clear storage.
A new UUID would make sense only for a deliberately new, unrelated output store.

It would also help if CADET-RDM detected this failure mode and printed a targeted message such as:

The output remote exists but is not a CADET-RDM output repository.
Run `cadetrdm output reseed` to initialize a fresh output main branch.

instead of surfacing only the missing .cadet-rdm-data.json exception.

Related documentation gap:

For GitHub-hosted LFS objects, rewriting history does not remove already uploaded LFS objects from storage.
Deleting and recreating the output repository is the documented cleanup path.
CADET-RDM documentation could mention that only a fresh metadata main should be pushed back in that workflow, not git push --all, because pushing all branches may restore the old LFS objects.