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/innercontext/models/product.py

@@ -2,7 +2,7 @@ from datetime import date, datetime
 from typing import ClassVar, Optional
 from uuid import UUID, uuid4
 
-from pydantic import model_validator
+from pydantic import field_validator, model_validator
 from sqlalchemy import JSON, Column, DateTime
 from sqlmodel import Field, Relationship, SQLModel
 
@@ -188,6 +188,13 @@ class Product(SQLModel, table=True):
 
     inventory: list["ProductInventory"] = Relationship(back_populates="product")
 
+    @field_validator("product_effect_profile", mode="before")
+    @classmethod
+    def coerce_effect_profile(cls, v: object) -> object:
+        if isinstance(v, dict):
+            return ProductEffectProfile(**v)
+        return v
+
     @model_validator(mode="after")
     def validate_business_rules(self) -> "Product":
         if (