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/static/index.html

@@ -229,6 +229,7 @@
       <div class="section-header">
         <h2 class="section-title">LLM swap</h2>
         <button id="open-download" class="btn small-btn">+ Download a new model</button>
+        <button id="open-local" class="btn small-btn">+ Add local model</button>
       </div>
 
       <dialog id="catalog-dialog" class="modal">
@@ -261,6 +262,37 @@
         </form>
       </dialog>
 
+      <dialog id="local-model-dialog" class="modal">
+        <form method="dialog" class="modal-form" id="local-model-form">
+          <h3>Add a local / fine-tuned model</h3>
+          <p class="muted small">For a model that lives as a directory on a Spark (e.g. a fine-tune), not a Hugging Face repo. The directory is bind-mounted into the vLLM container at the same path when you swap to it. It must already exist on the Spark.</p>
+          <label class="modal-row"><span>Key (URL-safe id)</span><input type="text" id="lm-key" required pattern="[a-zA-Z0-9_-]+"></label>
+          <label class="modal-row"><span>Display name</span><input type="text" id="lm-name" required></label>
+          <label class="modal-row"><span>Model directory (absolute path on the Spark)</span><input type="text" id="lm-path" required placeholder="e.g. /home/you/models/my-finetune"></label>
+          <label class="modal-row"><span>Chat template path (optional)</span><input type="text" id="lm-chat" placeholder="e.g. /home/you/models/my-finetune/chat_template.jinja"></label>
+          <label class="modal-row"><span>Size (GB)</span><input type="number" id="lm-size" step="0.1" min="0"></label>
+          <label class="modal-row"><span>Mode</span>
+            <select id="lm-mode">
+              <option value="solo">solo (Spark 1 only)</option>
+              <option value="cluster">cluster (both Sparks via Ray)</option>
+            </select>
+          </label>
+          <label class="modal-row"><span>Description (optional)</span><textarea id="lm-desc" rows="3"></textarea></label>
+          <fieldset class="modal-fieldset">
+            <legend>Default launch knobs</legend>
+            <label class="modal-row"><span>Max context (tokens)</span><input type="number" id="lm-mml" step="1024" min="1024" value="32768"></label>
+            <label class="modal-row"><span>GPU memory %</span><input type="range" id="lm-gmu" min="0.5" max="0.95" step="0.01" value="0.85"> <output id="lm-gmu-out">0.85</output></label>
+            <label class="modal-row inline"><input type="checkbox" id="lm-fst" checked> Fast safetensors loading</label>
+            <label class="modal-row inline"><input type="checkbox" id="lm-pcache" checked> Prefix caching</label>
+            <label class="modal-row inline"><input type="checkbox" id="lm-fp8" checked> FP8 KV cache</label>
+          </fieldset>
+          <div class="modal-actions">
+            <button type="button" id="lm-cancel" class="btn">Cancel</button>
+            <button type="submit" class="btn primary">Add local model</button>
+          </div>
+        </form>
+      </dialog>
+
       <dialog id="disk-delete-dialog" class="modal">
         <form method="dialog" class="modal-form">
           <h3>Delete model weights from disk?</h3>