Refactor(Structure): Move ADTs into adt/ folder, rename spel.rkt to main.rkt

New structure groups all ADT modules under adt/ directory, removing
redundant adt- prefix from filenames. Library names now read as
(pacman-project adt position) etc. All imports updated accordingly.

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

pacman-project/adt/key.rkt

@@ -0,0 +1,55 @@
+#lang r7rs
+
+(#%require (only racket/base random))
+
+;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
+;;                                Key ADT                                    ;;
+;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
+
+;; The key is placed at a random coin position in the maze. When Pac-Man
+;; picks it up, doors can be opened. Contains NO graphics code.
+
+(define-library (pacman-project adt key)
+  (import (scheme base)
+          (pacman-project constants)
+          (pacman-project adt position))
+  (export make-key)
+
+  (begin
+
+    ;; make-key :: maze -> key
+    ;; Creates a key and places it at a random coin position.
+    (define (make-key maze)
+      (let ((position #f)
+            (taken? #f))
+
+        ;; place-random! :: -> /
+        ;; Places the key on a random cell that contains a coin.
+        (define (place-random!)
+          (let loop ((attempts 0))
+            (if (>= attempts max-placement-attempts)
+                (error "No valid position found for key")
+                (let ((col (random 0 (maze 'cols)))
+                      (row (random 0 (maze 'rows))))
+                  (if ((maze 'coin?) row col)
+                      (begin
+                        (set! position (make-position row col))
+                        ((maze 'cell-set!) row col cell-type-key))
+                      (loop (+ attempts 1)))))))
+
+        ;; take! :: -> /
+        ;; Marks the key as taken.
+        (define (take!)
+          (set! taken? #t))
+
+        ;; Initialization: place the key immediately on creation.
+        (place-random!)
+
+        ;; dispatch-key :: symbol -> any
+        (define (dispatch-key msg)
+          (cond ((eq? msg 'position) position)
+                ((eq? msg 'taken?) taken?)
+                ((eq? msg 'take!) take!)
+                (else (error "Key ADT -- Unknown message:" msg))))
+
+        dispatch-key))))