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.

image/app/overrides.py

@@ -14,7 +14,7 @@ Shape:
     custom:
       - key: my-new-model
         display_name: My New Model (from download)
-        repo: my-org/my-model
+        repo: my-org/my-model        # an HF repo; OR set local_path instead (exactly one)
         size_gb: 20
         mode: solo
         description: null
@@ -25,6 +25,12 @@ Shape:
           fastsafetensors: true
           prefix_caching: true
           kv_cache_dtype: fp8
+      - key: my-finetune                       # a local/fine-tuned model (a directory on the Spark)
+        display_name: My Fine-tune
+        local_path: /home/you/models/my-finetune
+        size_gb: 59
+        mode: solo
+        vllm_args: [--chat-template=/home/you/models/my-finetune/chat_template.jinja]
 """
 from __future__ import annotations
 import os