feat(WP-0016/C1-C4): Layer 2 isolation and clean-base infrastructure

- Add Web/Controller/Prelude.hs (was missing; 8 controllers failed to import it)
- Add .ghci-core and scripts/compile-check-core to compile Layer 1+2 in
  isolation without loading Main.hs or any controller/view (Layer 3)
- Fix Application/Helper/BottleneckDetector.hs: replace coerce :: Id' -> UUID
  with unpackId (IHP Id' wraps a type family; Data.Coerce cannot cross it)
- Fix devenv.nix: add pkgs.nodePackages.tailwindcss so devenv process scripts
  find the tailwindcss binary (devenv v2 builds scripts with only local packages)

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

devenv.nix

@@ -15,6 +15,10 @@
   # GHC parallel module compilation is capped via -j1 in .ghci instead.
   env.GHCRTS = "-A32m -M2g";
 
+  # Make tailwindcss available in process scripts (devenv v2 builds process
+  # scripts with only packages declared here, not from flake ihp.packages).
+  packages = [ pkgs.nodePackages.tailwindcss ];
+
   # Tailwind CSS watcher — not part of IHP's core devenv module.
   processes.tailwind.exec = "tailwindcss -c tailwind/tailwind.config.js -i ./tailwind/app.css -o static/app.css --watch=always";
 }