- Enable RLS on all 6 tables
- inventory_items: shared inventory (all auth users can CRUD)
- products: read-only for users (service role for writes)
- tags: users can manage own tags, read all tags
- item_tags: auth users can tag/untag items
- units: users can create/manage custom units
- user_profiles: users manage only their own profile
- Comprehensive policy comments for documentation
Closes#14