feat: HUD

- add tower constants including cost, projectile stats, and duration
- add item buying timer for shop items
- add _draw_status_bar to handle dynamic HP rendering
- add _format_time for MM:SS display

src/hud.py

@@ -0,0 +1,23 @@
+import pygame
+from src.settings import (
+    HUD_FONT, HUD_FONT_SIZE, HUD_FONT_BOLD,
+    COLOR_HUD_TEXT, COLOR_HP_BAR_GREEN, COLOR_HP_BAR_RED, COLOR_HP_BAR_BG,
+    HUD_BAR_WIDTH, HUD_BAR_HEIGHT,
+    HUD_X_OFFSET, HUD_BAR_X, HUD_Y_DOOR, HUD_Y_ZOMBIE, HUD_Y_ECTS
+)
+
+# draw status bar (background bar and the colored hp bar)
+def _draw_status_bar(screen, x, y, current, max_val, color):
+    # bg bar is always the same
+    pygame.draw.rect(screen, COLOR_HP_BAR_BG, (x, y, HUD_BAR_WIDTH, HUD_BAR_HEIGHT))
+
+    # hp bar
+    if max_val > 0:
+        hp_width = (current / max_val) * HUD_BAR_WIDTH
+        pygame.draw.rect((screen, color), (x, y, hp_width, HUD_BAR_HEIGHT))
+
+# time formatter for MM:SS
+def _format_time(total_seconds):
+    mins = total_seconds // 60
+    secs = total_seconds % 60
+    return f"TIME {mins:02}:{secs:02}"