feat: add shared pathway query functions for Dash data access (Task 1.1)

Extract load_data() and load_pathway_data() logic from Reflex AppState
into standalone functions in src/data_processing/pathway_queries.py.
Create thin dash_app/data/queries.py wrapper with DB_PATH resolution.

dash_app/data/queries.py

@@ -0,0 +1,37 @@
+"""
+Thin wrapper around shared pathway query functions.
+
+Resolves the database path relative to this file's location and delegates
+to the shared functions in src/data_processing/pathway_queries.py.
+"""
+
+from pathlib import Path
+from typing import Optional
+
+from data_processing.pathway_queries import (
+    load_initial_data as _load_initial_data,
+    load_pathway_nodes as _load_pathway_nodes,
+)
+
+DB_PATH = Path(__file__).resolve().parents[2] / "data" / "pathways.db"
+
+
+def load_initial_data() -> dict:
+    """Load reference data (drugs, directorates, indications, refresh info)."""
+    return _load_initial_data(DB_PATH)
+
+
+def load_pathway_data(
+    filter_id: str = "all_6mo",
+    chart_type: str = "directory",
+    selected_drugs: Optional[list[str]] = None,
+    selected_directorates: Optional[list[str]] = None,
+) -> dict:
+    """Load pre-computed pathway nodes with optional filters."""
+    return _load_pathway_nodes(
+        DB_PATH,
+        filter_id=filter_id,
+        chart_type=chart_type,
+        selected_drugs=selected_drugs,
+        selected_directorates=selected_directorates,
+    )