feat(ml): default to SigLIP 2 (new installs) + model dropdown, no free-text (#1203)

- Migration 0069: new installs default to SigLIP 2 (so400m, 512px, 1152-d drop-in)
  — UPDATE applies ONLY where no image is embedded yet (fresh install), so an
  existing library is NOT silently invalidated; it switches deliberately via the
  dropdown → Re-embed → Retrain. Column server_defaults moved to SigLIP 2.
- GET /api/ml/embedder-models: server-authoritative supported list (SigLIP 2 512
  recommended / 384 faster / SigLIP 1 384 original) so the UI never free-types.
- GpuAgentCard: the two name/version text fields → a single model dropdown;
  Save sets name+version from the picked option (the current model is always
  selectable even if off-list).
- embedder.py DEFAULT_MODEL_NAME unchanged (stays the baked local-dir SigLIP 1)
  to avoid a local-dir/weights mismatch; SigLIP 2 loads by HF name, cached on the
  ml-worker's persistent HF_HOME.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Ttrj5P7upUTueSfoJcxEqa

tests/test_api_ml_admin.py

@@ -34,25 +34,34 @@ async def test_get_and_patch_settings(client):
 
 
 @pytest.mark.asyncio
-async def test_embedder_model_settable_and_empty_rejected(client):
-    # #1190: the embedder model name + version are operator-settable (a swap),
-    # and neither may be blanked.
+async def test_embedder_model_default_settable_and_empty_rejected(client):
+    # #1203: fresh installs default to SigLIP 2 (migration 0069, no embeddings).
+    # The model is operator-settable (a swap) and neither field may be blanked.
     body = await (await client.get("/api/ml/settings")).get_json()
-    assert body["embedder_model_name"] == "google/siglip-so400m-patch14-384"
+    assert body["embedder_model_name"] == "google/siglip2-so400m-patch16-512"
 
     ok = await client.patch("/api/ml/settings", json={
-        "embedder_model_name": "google/siglip2-so400m-patch16-512",
-        "embedder_model_version": "siglip2-so400m-patch16-512",
+        "embedder_model_name": "google/siglip-so400m-patch14-384",
+        "embedder_model_version": "siglip-so400m-patch14-384",
     })
     assert ok.status_code == 200
     out = await ok.get_json()
-    assert out["embedder_model_name"] == "google/siglip2-so400m-patch16-512"
-    assert out["embedder_model_version"] == "siglip2-so400m-patch16-512"
+    assert out["embedder_model_name"] == "google/siglip-so400m-patch14-384"
 
     bad = await client.patch("/api/ml/settings", json={"embedder_model_name": "  "})
     assert bad.status_code == 400
 
 
+@pytest.mark.asyncio
+async def test_embedder_models_list(client):
+    # #1203: the dropdown reads the supported-model list from the server.
+    body = await (await client.get("/api/ml/embedder-models")).get_json()
+    assert any(
+        m["name"] == "google/siglip2-so400m-patch16-512" for m in body["models"]
+    )
+    assert all({"name", "version", "label"} <= set(m) for m in body["models"])
+
+
 @pytest.mark.asyncio
 async def test_video_settings_default_and_patch(client):
     """#747: video frame-sampling knobs are exposed + patchable."""