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>

scripts/compile-check-core

@@ -0,0 +1,20 @@
+#!/usr/bin/env bash
+# scripts/compile-check-core
+#
+# Verify Layer 1 + Layer 2 compile cleanly in isolation — WITHOUT loading
+# any controller, view, or Main.hs. Use this to establish and confirm the
+# clean base before working on Layer 3 (controllers/views).
+#
+# Usage (inside devenv shell):
+#   scripts/compile-check-core         # interactive
+#   scripts/compile-check-core --bg    # write to log only
+#
+# Once this reports "Ok, N modules loaded" with no errors, the core is clean.
+set -euo pipefail
+LOGFILE="${IHUB_COMPILE_LOG:-/tmp/ihub-core-errors.txt}"
+: > "$LOGFILE"
+echo "[compile-check-core] Writing to $LOGFILE"
+exec ghcid \
+  --no-title \
+  --outputfile "$LOGFILE" \
+  --command "ghci -ghci-script .ghci-core"