feat: retention funnel chart tab with treatment line depth (Task C.1)

dash_app/data/queries.py

@@ -24,6 +24,7 @@ from data_processing.pathway_queries import (
     get_trust_heatmap as _get_trust_heatmap,
     get_trust_durations as _get_trust_durations,
     get_directorate_summary as _get_directorate_summary,
+    get_retention_funnel as _get_retention_funnel,
 )
 
 DB_PATH = Path(__file__).resolve().parents[2] / "data" / "pathways.db"
@@ -180,3 +181,16 @@ def get_directorate_summary(
 ) -> list[dict]:
     """Per-directorate summary (name, patient count, drug count) for landing cards."""
     return _get_directorate_summary(DB_PATH, date_filter_id, chart_type)
+
+
+# --- Retention funnel (Phase C) ---
+
+
+def get_retention_funnel(
+    date_filter_id: str = "all_6mo",
+    chart_type: str = "directory",
+    directory: Optional[str] = None,
+    trust: Optional[str] = None,
+) -> list[dict]:
+    """Patient retention by treatment line depth."""
+    return _get_retention_funnel(DB_PATH, date_filter_id, chart_type, directory, trust)