Add missing packages and paths for ghci-based testing

devenv-module.nix:
- Add slugger, megaparsec, cryptohash, pwstore-fast, vault to
  ghcWithPackages so ghci can load IHP modules directly

.ghci:
- Add ihp-imagemagick and ihp-hspec to include paths

This enables running tests via ghci:
  direnv exec . bash -c 'echo -e ":l ihp-ide/Test/Main.hs\nmain" | ghci'

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: mpscholten

.ghci

@@ -3,6 +3,8 @@
 :set -iihp
 :set -iihp-ide
 :set -iihp-ssc
+:set -iihp-imagemagick
+:set -iihp-hspec
 :set -iwai-asset-path
 :set -iwai-flash-messages
 :set -threaded

devenv-module.nix

@@ -116,6 +116,12 @@ that is defined in flake-module.nix
                         ihp-hsx
                         ihp-postgresql-simple-extra
 
+                        # Packages needed for ghci to load IHP modules
+                        slugger
+                        megaparsec
+                        cryptohash
+                        pwstore-fast
+                        vault
 
                         http-streams
                         HsOpenSSL