fix(clustering): route embeddings through LiteLLM instead of Ollama directly

The old code called Ollama's /api/embeddings one task at a time, which caused
silent fallback to project-based grouping when host.docker.internal:11434 was
unreachable from the ml-serving container.

- Switch to LiteLLM /embeddings (model alias "embedder") as primary path
- Batch all task contents in one request instead of N serial calls
- Fall back to Ollama /api/embed (updated to current API) when LITELLM_URL is absent
- Update tests to mock _embed_batch instead of the removed _embed

Fixes #123

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

ml/agents/tests/test_clustering.py

@@ -9,7 +9,7 @@ sys.path.insert(0, os.path.join(os.path.dirname(__file__), "..", "..", ".."))
 
 from unittest.mock import patch
 
-from ml.agents.clustering import cluster_tasks, Cluster, _greedy_cluster, _cosine
+from ml.agents.clustering import cluster_tasks, Cluster, _greedy_cluster, _cosine, _embed_batch
 
 
 # ── helpers ──────────────────────────────────────────────────────────────────
@@ -89,8 +89,8 @@ class TestClusterTasks:
         result = cluster_tasks([])
         assert result == []
 
-    def test_fallback_when_ollama_unavailable(self):
-        with patch("ml.agents.clustering._embed", return_value=None):
+    def test_fallback_when_embed_unavailable(self):
+        with patch("ml.agents.clustering._embed_batch", return_value=None):
             tasks = [_task("A", "p1"), _task("B", "p2"), _task("C", "p1")]
             clusters = cluster_tasks(tasks)
         assert len(clusters) == 2
@@ -98,7 +98,7 @@ class TestClusterTasks:
         assert "p1" in labels and "p2" in labels
 
     def test_fallback_groups_by_project(self):
-        with patch("ml.agents.clustering._embed", return_value=None):
+        with patch("ml.agents.clustering._embed_batch", return_value=None):
             tasks = [_task("A", "work")] * 3 + [_task("B", "home")] * 2
             clusters = cluster_tasks(tasks)
         by_label = {c.label: c.task_count for c in clusters}
@@ -107,7 +107,7 @@ class TestClusterTasks:
 
     def test_tasks_without_content_go_to_other(self):
         v = [1.0, 0.0]
-        with patch("ml.agents.clustering._embed", return_value=v):
+        with patch("ml.agents.clustering._embed_batch", return_value=[v]):
             tasks = [_task("Has content"), {"is_overdue": False}]
             clusters = cluster_tasks(tasks)
         labels = {c.label for c in clusters}
@@ -116,8 +116,8 @@ class TestClusterTasks:
     def test_semantic_clustering_groups_similar(self):
         v_work = [1.0, 0.0, 0.0]
         v_home = [0.0, 1.0, 0.0]
-        side_effects = [v_work, v_work, v_home, v_home]
-        with patch("ml.agents.clustering._embed", side_effect=side_effects):
+        batch_result = [v_work, v_work, v_home, v_home]
+        with patch("ml.agents.clustering._embed_batch", return_value=batch_result):
             tasks = [
                 _task("Write report"),
                 _task("Review PR"),