fix(nav): AcademicWeek children + days support in graph tree API

- AcademicWeek now returns has_children=true in both /calendar/academic
  endpoint and _get_children_for_node for AcademicTerm case
- Added AcademicWeek case to _get_children_for_node: queries
  ACADEMIC_WEEK_HAS_ACADEMIC_DAY relationships to return AcademicDay children
- Academic calendar can now expand weeks to show individual days

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

routers/database/tools/graph_tree_router.py

@@ -489,7 +489,33 @@ def _get_children_for_node(
             logger.warning(f"AcademicYear children failed: {e}")
         return []
 
-    # AcademicTerm → weeks
+    # AcademicWeek → days
+    if node_type == "AcademicWeek" and neo4j_db_name:
+        try:
+            with driver_tools.get_session(database=neo4j_db_name) as session:
+                result = session.run(
+                    "MATCH (w:AcademicWeek {uuid_string: })"
+                    "-[:ACADEMIC_WEEK_HAS_ACADEMIC_DAY]->(d:AcademicDay) "
+                    "RETURN d ORDER BY d.date",
+                    id=neo4j_node_id,
+                )
+                days = [
+                    {
+                        "neo4j_node_id": r["d"]["uuid_string"],
+                        "label": r["d"].get("date", ""),
+                        "node_type": "AcademicDay",
+                        "neo4j_db_name": neo4j_db_name,
+                        "is_section": False,
+                        "has_children": False,
+                    }
+                    for r in result
+                ]
+                return days
+        except Exception as e:
+            logger.warning(f"AcademicWeek children failed: {e}")
+        return []
+
+        # AcademicTerm → weeks
     if node_type == "AcademicTerm" and neo4j_db_name:
         try:
             with driver_tools.get_session(database=neo4j_db_name) as session:
@@ -506,7 +532,7 @@ def _get_children_for_node(
                         "node_type": "AcademicWeek",
                         "neo4j_db_name": neo4j_db_name,
                         "is_section": False,
-                        "has_children": False,
+                        "has_children": True,
                     }
                     for r in result
                 ]
@@ -622,7 +648,7 @@ async def get_academic_calendar(credentials: dict = Depends(SupabaseBearer())) -
                         "node_type": "AcademicWeek",
                         "neo4j_db_name": institute_db,
                         "is_section": False,
-                        "has_children": False,
+                        "has_children": True,
                     } for w in s2.run(
                         "MATCH (t:AcademicTerm {uuid_string: $tid})-[:ACADEMIC_TERM_HAS_ACADEMIC_WEEK]->(w:AcademicWeek) "
                         "RETURN w ORDER BY toInteger(w.academic_week_number)",