Add ghost CPUs with original Pac-Man AI targeting

Implement four ghosts (Blinky, Pinky, Inky, Clyde) with authentic
Pac-Man AI: Blinky chases directly, Pinky targets 2 tiles ahead
(with original up-direction bug), Inky uses vector doubling from
Blinky, Clyde switches to scatter within 8-tile radius.

Includes chase/scatter mode cycling, ghost house exit with staggered
delays, directional sprite rendering with animation, and ghost-pacman
collision detection.

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

pacman-project/constants.rkt

@@ -33,9 +33,54 @@
           sprite-scale-pacman
           sprite-scale-key
           sprite-scale-key-ui
+          sprite-scale-ghost
 
           ;; Movement
           pacman-speed-ms
+          ghost-speed-ms
+
+          ;; Ghost house
+          ghost-house-door-row
+          ghost-house-door-col-left
+          ghost-house-door-col-right
+          ghost-house-exit-row
+          ghost-house-exit-col
+
+          ;; Ghost start positions
+          blinky-start-row
+          blinky-start-col
+          pinky-start-row
+          pinky-start-col
+          inky-start-row
+          inky-start-col
+          clyde-start-row
+          clyde-start-col
+
+          ;; Ghost scatter corners
+          blinky-scatter-row
+          blinky-scatter-col
+          pinky-scatter-row
+          pinky-scatter-col
+          inky-scatter-row
+          inky-scatter-col
+          clyde-scatter-row
+          clyde-scatter-col
+
+          ;; Ghost house exit delays (ms)
+          pinky-exit-delay
+          inky-exit-delay
+          clyde-exit-delay
+
+          ;; Ghost mode durations (ms)
+          scatter-duration-1
+          chase-duration-1
+          scatter-duration-2
+          chase-duration-2
+          scatter-duration-3
+
+          ;; Ghost AI
+          clyde-shy-distance
+          pinky-look-ahead
 
           ;; Animation
           animation-interval-ms
@@ -123,9 +168,54 @@
     (define sprite-scale-pacman 1.5)
     (define sprite-scale-key 1.5)
     (define sprite-scale-key-ui 3)
+    (define sprite-scale-ghost 1.5)
 
     ;; Movement speed: time between automatic movement ticks
     (define pacman-speed-ms 200)
+    (define ghost-speed-ms 220)
+
+    ;; Ghost house position (door and exit point above door)
+    (define ghost-house-door-row 12)
+    (define ghost-house-door-col-left 13)
+    (define ghost-house-door-col-right 14)
+    (define ghost-house-exit-row 11)
+    (define ghost-house-exit-col 14)
+
+    ;; Ghost start positions
+    (define blinky-start-row 11)
+    (define blinky-start-col 14)
+    (define pinky-start-row 14)
+    (define pinky-start-col 13)
+    (define inky-start-row 14)
+    (define inky-start-col 11)
+    (define clyde-start-row 14)
+    (define clyde-start-col 16)
+
+    ;; Ghost scatter target corners
+    (define blinky-scatter-row 0)
+    (define blinky-scatter-col 27)
+    (define pinky-scatter-row 0)
+    (define pinky-scatter-col 0)
+    (define inky-scatter-row 30)
+    (define inky-scatter-col 27)
+    (define clyde-scatter-row 30)
+    (define clyde-scatter-col 0)
+
+    ;; Ghost house exit delays (ms) — staggered release
+    (define pinky-exit-delay 2000)
+    (define inky-exit-delay 5000)
+    (define clyde-exit-delay 8000)
+
+    ;; Ghost mode durations (ms) — scatter/chase alternation
+    (define scatter-duration-1 7000)
+    (define chase-duration-1 20000)
+    (define scatter-duration-2 7000)
+    (define chase-duration-2 20000)
+    (define scatter-duration-3 5000)
+
+    ;; Ghost AI parameters
+    (define clyde-shy-distance 8)
+    (define pinky-look-ahead 2)
 
     ;; Animation timing
     (define animation-interval-ms 100)