v0.23.0:0 - local / fine-tuned model support

Add models that live as a directory on a Spark (e.g. LoRA-merged fine-tunes),
not just Hugging Face repos.

- ModelDef gains local_path; a model must set exactly one of repo / local_path.
  The validator also enforces the local-path whitelist and that any
  --chat-template lives inside local_path (only that dir is mounted).
- build_launch_command bind-mounts the dir into the vLLM container at the SAME
  host==container path via the launch script's VLLM_SPARK_EXTRA_DOCKER_ARGS hook,
  then `vllm serve <dir>`. No launch-cluster.sh change (verified the upstream
  expands that var unquoted; contract noted in runbook.md).
- shellsafe.validate_local_path: absolute path, charset whitelist, no '.'/'..'.
- POST /api/models validates the full entry via ModelDef before persisting, so a
  bad entry can't be written and then break catalog load; _merge_overrides skips
  an invalid override entry instead of failing the whole catalog.
- disk.py size-probes a local path with du; disk-delete refused for local models.
- UI: "+ Add local model" dialog, `local` badge, path shown instead of an HF
  link, delete button hidden for local models.
- Tests: local launch + injection round-trip, chat-template location, traversal,
  exactly-one-source, _merge_overrides skip-invalid (94 pass). Reviewer-agent
  pass; findings addressed.

runbook.md

@@ -60,6 +60,12 @@ The **Update** button runs `git fetch && git reset --hard origin/<branch> && doc
 
 If `description` is omitted, the card simply hides that section — no need to populate it for every model. Keep descriptions generic (not user-specific) so the catalog stays portable.
 
+### Local / fine-tuned models (v0.23.0+)
+
+A model that lives as a directory on a Spark (e.g. a LoRA-merged fine-tune) instead of an HF repo: use the **"+ Add local model"** button under LLM swap (or a `custom:` entry with `local_path` instead of `repo` in the override YAML). The directory must already exist on the Spark; only its parent dir is mounted, so a `--chat-template` must live **inside** `local_path`.
+
+**Load-bearing contract:** on swap, spark-control prefixes the launch with `VLLM_SPARK_EXTRA_DOCKER_ARGS="-v <path>:<path>"` so `launch-cluster.sh` bind-mounts the dir into the vLLM container at the same path. This relies on the upstream `eugr/spark-vllm-docker` `launch-cluster.sh` expanding `$VLLM_SPARK_EXTRA_DOCKER_ARGS` **unquoted** into its `docker run` (verified against the on-Spark script 2026-06-17: line ~11 appends it to `DOCKER_ARGS`, used unquoted in `docker run`). If a future upstream version quotes that variable, local-model mounts would silently fail — re-check this before pulling launch-cluster.sh updates.
+
 ## Manual swap fallback
 
 If the UI is unavailable and you need to swap by hand: