fix(WP-0016): Layer 3 compilation fixes — Sessions auth, Widgets import consolidation, Scientific type

- Sessions: replace raw authenticate/unsetSession with IHP login/logout/verifyPassword
- Widgets/New, Widgets/Show: consolidate imports to Web.View.Prelude
- Widgets/Show: unwrap Id newtype for childrenOf comparison, Double → Scientific in renderSignalValue

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

Web/View/Widgets/New.hs

@@ -1,10 +1,6 @@
 module Web.View.Widgets.New where
 
-import Web.Types
-import Generated.Types
-import IHP.Prelude
-import IHP.ViewPrelude
-import Web.Routes ()
+import Web.View.Prelude
 
 data NewView = NewView
     { widget       :: !Widget