feat: add maintenance tree_type with db migration and tests

- Expand ck_trees_tree_type CHECK constraint to include 'maintenance'
- Add 'maintenance' to TreeType Literal in schemas
- Treat maintenance trees as procedural in can_publish_tree validation
- Alembic migration 0f1ca2af3647 drops and recreates the constraint
- Two integration tests: create and filter by tree_type=maintenance

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

backend/tests/test_maintenance_tree_type.py

@@ -0,0 +1,52 @@
+"""Tests for maintenance tree type."""
+import pytest
+from httpx import AsyncClient
+
+
+@pytest.mark.asyncio
+async def test_create_maintenance_tree(client: AsyncClient, auth_headers: dict):
+    """Maintenance tree type is accepted by the API."""
+    resp = await client.post(
+        "/api/v1/trees",
+        json={
+            "name": "Update FSLogix",
+            "description": "Monthly FSLogix update procedure",
+            "tree_type": "maintenance",
+            "tree_structure": {
+                "steps": [
+                    {"id": "step-1", "type": "procedure_step", "title": "Download installer",
+                     "description": "Get latest FSLogix from Microsoft", "content_type": "action"},
+                    {"id": "step-end", "type": "procedure_end", "title": "Complete"},
+                ]
+            },
+        },
+        headers=auth_headers,
+    )
+    assert resp.status_code == 201, resp.text
+    data = resp.json()
+    assert data["tree_type"] == "maintenance"
+
+
+@pytest.mark.asyncio
+async def test_list_maintenance_trees_filter(client: AsyncClient, auth_headers: dict):
+    """Filtering by tree_type=maintenance returns only maintenance trees."""
+    await client.post(
+        "/api/v1/trees",
+        json={
+            "name": "Maintenance Only",
+            "tree_type": "maintenance",
+            "tree_structure": {
+                "steps": [
+                    {"id": "s1", "type": "procedure_step", "title": "Step",
+                     "description": "Do it", "content_type": "action"},
+                    {"id": "end", "type": "procedure_end", "title": "Done"},
+                ]
+            },
+        },
+        headers=auth_headers,
+    )
+    resp = await client.get("/api/v1/trees?tree_type=maintenance", headers=auth_headers)
+    assert resp.status_code == 200
+    trees = resp.json()
+    assert all(t["tree_type"] == "maintenance" for t in trees)
+    assert len(trees) >= 1