fix(ml): align tagger + downloader with Camie v2 actual layout (model.onnx -> camie-tagger-v2.onnx + JSON metadata + ImageNet preprocessing + sigmoid on refined output)

The HF repo Camais03/camie-tagger-v2 has camie-tagger-v2.onnx (789 MB)
+ camie-tagger-v2-metadata.json (7.77 MB) at root, NOT model.onnx +
selected_tags.csv. Tags ship as nested JSON (dataset_info.tag_mapping)
not CSV. Per the published onnx_inference.py reference: input is NCHW
not NHWC, normalize with ImageNet mean/std, pad-square color (124,116,
104), sigmoid the second output (refined predictions) not the first.

Operator hit this during the IR migration ML backfill — download_models
silently fetched only 3 json files (allow_patterns matched nothing
useful), tagger.load() then raised RuntimeError. Fetched the actual
v2 layout via WebFetch, rewrote tagger to match published reference.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

backend/app/scripts/download_models.py

@@ -25,12 +25,31 @@ def _snapshot(repo_id: str, dest: Path, allow_patterns: list[str] | None) -> Non
 
 
 def ensure_camie() -> None:
+    """Fetch Camie v2 weights + metadata.
+
+    v2 layout (HuggingFace Camais03/camie-tagger-v2): the ONNX file is
+    named camie-tagger-v2.onnx (not model.onnx) and tags ship inside
+    camie-tagger-v2-metadata.json (not selected_tags.csv). Both at root.
+    The repo also contains app/, game/, training/, images/ subdirs full
+    of setup/demo files we don't need — allow_patterns scopes the fetch
+    to just the inference essentials (~790 MB instead of ~2 GB).
+    """
     dest = MODEL_ROOT / "camie"
-    if (dest / "model.onnx").is_file() and (dest / "selected_tags.csv").is_file():
+    model_file = dest / "camie-tagger-v2.onnx"
+    meta_file = dest / "camie-tagger-v2-metadata.json"
+    if model_file.is_file() and meta_file.is_file():
         print(f"[download_models] Camie present at {dest}")
         return
     print(f"[download_models] Fetching {CAMIE_REPO} -> {dest}")
-    _snapshot(CAMIE_REPO, dest, ["model.onnx", "selected_tags.csv", "*.json"])
+    _snapshot(
+        CAMIE_REPO, dest,
+        [
+            "camie-tagger-v2.onnx",
+            "camie-tagger-v2-metadata.json",
+            "config.json",
+            "config.yaml",
+        ],
+    )
 
 
 def ensure_siglip() -> None: