fix: resolve frontend/backend integration bugs

- Rename skincare route prefix /skin-snapshots → /skincare to match API client
- Add redirect_slashes=False to FastAPI app; change collection routes from "/" to ""
  to eliminate 307 redirects on POST/GET without trailing slash
- Fix redirect() inside try/catch in products/new and routines/new server actions
  (SvelteKit redirect() throws and was being caught as a 500 error)
- Eagerly load inventory and steps relationships via explicit SELECT + model_dump(mode="json"),
  working around SQLModel 0.0.37 not serializing Relationship fields in response_model
- Add field_validator for product_effect_profile to coerce DB-returned dict → ProductEffectProfile,
  eliminating Pydantic serializer warning
- Update all tests to use routes without trailing slash

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

backend/tests/test_skincare.py

@@ -2,7 +2,7 @@ import uuid
 
 
 def test_create_snapshot_minimal(client):
-    r = client.post("/skin-snapshots/", json={"snapshot_date": "2026-02-26"})
+    r = client.post("/skincare", json={"snapshot_date": "2026-02-26"})
     assert r.status_code == 201
     data = r.json()
     assert "id" in data
@@ -12,7 +12,7 @@ def test_create_snapshot_minimal(client):
 
 def test_create_snapshot_full(client):
     r = client.post(
-        "/skin-snapshots/",
+        "/skincare",
         json={
             "snapshot_date": "2026-02-20",
             "overall_state": "good",
@@ -39,22 +39,22 @@ def test_create_snapshot_full(client):
 
 def test_create_snapshot_invalid_state(client):
     r = client.post(
-        "/skin-snapshots/",
+        "/skincare",
         json={"snapshot_date": "2026-02-26", "overall_state": "stellar"},
     )
     assert r.status_code == 422
 
 
 def test_list_snapshots_empty(client):
-    r = client.get("/skin-snapshots/")
+    r = client.get("/skincare")
     assert r.status_code == 200
     assert r.json() == []
 
 
 def test_list_filter_date_range(client):
-    client.post("/skin-snapshots/", json={"snapshot_date": "2026-01-01"})
-    client.post("/skin-snapshots/", json={"snapshot_date": "2026-06-01"})
-    r = client.get("/skin-snapshots/?from_date=2026-05-01&to_date=2026-12-31")
+    client.post("/skincare", json={"snapshot_date": "2026-01-01"})
+    client.post("/skincare", json={"snapshot_date": "2026-06-01"})
+    r = client.get("/skincare?from_date=2026-05-01&to_date=2026-12-31")
     assert r.status_code == 200
     data = r.json()
     assert len(data) == 1
@@ -63,14 +63,14 @@ def test_list_filter_date_range(client):
 
 def test_list_filter_overall_state(client):
     client.post(
-        "/skin-snapshots/",
+        "/skincare",
         json={"snapshot_date": "2026-02-10", "overall_state": "good"},
     )
     client.post(
-        "/skin-snapshots/",
+        "/skincare",
         json={"snapshot_date": "2026-02-11", "overall_state": "poor"},
     )
-    r = client.get("/skin-snapshots/?overall_state=poor")
+    r = client.get("/skincare?overall_state=poor")
     assert r.status_code == 200
     data = r.json()
     assert len(data) == 1
@@ -78,31 +78,31 @@ def test_list_filter_overall_state(client):
 
 
 def test_get_snapshot(client):
-    r = client.post("/skin-snapshots/", json={"snapshot_date": "2026-02-26"})
+    r = client.post("/skincare", json={"snapshot_date": "2026-02-26"})
     sid = r.json()["id"]
-    r2 = client.get(f"/skin-snapshots/{sid}")
+    r2 = client.get(f"/skincare/{sid}")
     assert r2.status_code == 200
     assert r2.json()["id"] == sid
 
 
 def test_get_snapshot_not_found(client):
-    r = client.get(f"/skin-snapshots/{uuid.uuid4()}")
+    r = client.get(f"/skincare/{uuid.uuid4()}")
     assert r.status_code == 404
 
 
 def test_update_snapshot_state(client):
-    r = client.post("/skin-snapshots/", json={"snapshot_date": "2026-02-26"})
+    r = client.post("/skincare", json={"snapshot_date": "2026-02-26"})
     sid = r.json()["id"]
-    r2 = client.patch(f"/skin-snapshots/{sid}", json={"overall_state": "excellent"})
+    r2 = client.patch(f"/skincare/{sid}", json={"overall_state": "excellent"})
     assert r2.status_code == 200
     assert r2.json()["overall_state"] == "excellent"
 
 
 def test_update_snapshot_concerns(client):
-    r = client.post("/skin-snapshots/", json={"snapshot_date": "2026-02-26"})
+    r = client.post("/skincare", json={"snapshot_date": "2026-02-26"})
     sid = r.json()["id"]
     r2 = client.patch(
-        f"/skin-snapshots/{sid}",
+        f"/skincare/{sid}",
         json={"active_concerns": ["dehydration", "redness"]},
     )
     assert r2.status_code == 200
@@ -113,20 +113,20 @@ def test_update_snapshot_concerns(client):
 
 def test_update_snapshot_not_found(client):
     r = client.patch(
-        f"/skin-snapshots/{uuid.uuid4()}", json={"overall_state": "good"}
+        f"/skincare/{uuid.uuid4()}", json={"overall_state": "good"}
     )
     assert r.status_code == 404
 
 
 def test_delete_snapshot(client):
-    r = client.post("/skin-snapshots/", json={"snapshot_date": "2026-02-26"})
+    r = client.post("/skincare", json={"snapshot_date": "2026-02-26"})
     sid = r.json()["id"]
-    r2 = client.delete(f"/skin-snapshots/{sid}")
+    r2 = client.delete(f"/skincare/{sid}")
     assert r2.status_code == 204
-    r3 = client.get(f"/skin-snapshots/{sid}")
+    r3 = client.get(f"/skincare/{sid}")
     assert r3.status_code == 404
 
 
 def test_delete_snapshot_not_found(client):
-    r = client.delete(f"/skin-snapshots/{uuid.uuid4()}")
+    r = client.delete(f"/skincare/{uuid.uuid4()}")
     assert r.status_code == 404